Spondylus arcuatus (Catullo, 1834)
CATULLO, T. A. 1834. Memoria geognostico-zoologica sopra alcune conchiglie fossili del calcarejurese che si eleva presso il Lago di Santa Croce nel territorio di Belluno. Nuovi saggi della Imperiale regia Accademia di scienze, lettere ed arte in Padova, 4: 1-20, pls. 1, 2. [p. 17, pl. 2, fig. 6]
1834 Podopsis arcuata Catullo, 1834
T. A. Catullo, 1834, plate 2.
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«Testa longitudinali, cuneata, incurva, crassissima; striis longitudinalibus crebris; nate majore prominente, non inflexo.
Non è la Podopsis truncata di Lamarck, perchè questa ha la valva inferiore più larga, meno turgida, e meno incurvata della nostra, la quale somiglierebbe piuttosto ad una Grifea. S'i discosta però dalle Grifeeper non avere il beccuccio cardinale della valva inferiore incurvato·a spirale, e per essere longiludinalmente striata alla foggia dei pellini. La valva superiore, o più piccola, rimane nascosta nella ròccia; e la inferiore comparisce segnata per lungo da strie molto sottili, ma nondimeno elevate abbastanza per poterle senza stento numerare. Lunghezza poll. l. lin. 8, larghezza del margine superiore polI. I. lin. 3.»
TOMMASO ANTONIO CATULLO, 1834
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«Spondylus (S.) siccus can be differentiated from European species that have both primary and secondary radial costae, such as S. fimbriatus Goldfuss 1835, S. arcuatus (Catullo, 1834), S. truncatus (Lamark, 1819), and S. latus (Sowerby, 1815), by its having a fewer secondary ribs intercalated between the primary costae.»
ELDER, W. P. 1996. Bivalves and gastropods from the Middle Campanian Anacacho Limestone, south central Texas. Journal of Paleontology, 70 (2): 247-271, figs. 1-8. [p. 256]
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«Emended diagnosis: Large Spondylus species, with elongate moderately convex right valve and suborbicular-suboval almost flat left valve. Ornamentation changes during ontogeny. On large specimens, superimposed on simple diverging ribs, strong radial folds are formed; they seem to consist of fasciculated ribs on the central part of the disc, but occasionally cross the diverging ornamentation obliquely towards the side margins.
Description: Left valve is generally flat but the initial stage is irregularly gibbous because it is adapted to the shape of the attached part of the right valve (PI. XII, figs 2,4,5,7,8).
Early growth stages of left valve are suborbicular and covered with numerous subequal radial ribs of which some are more strongly developed than others, depending also on the preservation state. Ribs are unequal on the outside of the completely preserved shell, but on specimens with the outer shell layer removed every fourth or fifth rib is more strongly developed. Somewhat later growth stages develop radial folds, with about 7 to 8 narrow ribs in between two folds. The folds irregularly increase in width and height on the oldest growth stages, and several ribs which were intercalated between two narrow folds on the previous growth stage are now included in the radial folds (on the median part of the disc; PI. XII, fig. 8). On the anterior and posterior sides of the disc the folds sometimes obliquely intersect the ribs, which in turn on the sides of the disc diverge and are less strongly developed (PI. XII, fig. 7). The number of ribs varies but on an average young left valve 80 to 85 were counted. The diverging ornamentation is most clearly visible on the auricles. The anterior triangular and obtuse-angled auricle is small but clearly delimited from the disc, whereas the posterior auricle has a long side margin and continues seemingly without clear limit into the posterior marginal area. Early stages of right valve were attached to the substrate and therefore have no specific ornamentation. Further growth stages of this valve are, as on the left valves, ornamented with a diverging rib pattern, overlain by a radial ornamentation system. It consists mainly of 6-8 small ribs separated with a wider furrow from the next rib group. Such deeper furrows are present in equal number to the folds on the left valve. On the sides of the disc diverging ribs can be seen as on the left valves. No auricles are visible, but the triangular cardinal area is strongly developed. On the oldest growth stages - as described for the left valve - the right valve is covered by wide folds which assemble several small ribs and are of varying width. On both valves occasional commarginal growth interruptions are seen: rarely they form small knobs at the intersection points with the radial ribs. Attachment scars on the right valve show different patterns; on some specimens the ornamentation of a hippuritid can clearly be recognised in the attachment area (PI. XIII, fig. 16). In Text-fig. 10 the L/H ratios for right and left valves from the type locality are illustrated. Considering the small size of the studied sample the regression lines are obviously only indicative.
Discussion: Spondylus arcuatus is an unusual spondylid, and we have not been able to find any Cretaceous species which resemble it. The only taxon found in literature which seems somewhat comparable in shape is Sp. royanus d'Orbigny, 1847 (from the Campanian at Royan); the holotype is a very poorly preserved specimen and it lacks any real similarity with the figure in the Paléontologie française; therefore Sp. royanus could at best be considered a nomen dubium.
Spondylus arcuatus differs from Sp. requienianus Matheron, 1843, found in the same association from Pinei (PI. XIII, figs 4-15b), by its size and rib development: Sp. arcuatus can reach very large sizes and is covered with numerous unequal ribs and folds, whereas the generally much smaller Sp. requienianus only has numerous equal ribs. Yet, both seem to lack spines and the early growth stages of Sp. arcuatus could be taken for Sp. requienianus when the ribs are still more or less subequaI. Despite Futterer (1892 [1], p. 78) who placed Catullo's species in the possible synonymy of Sp. requienianus Matheron, 1843, we think that this synonymy is untenable (anyway Sp. arcuatus would have priority over Sp. requienianus). Other large spondylids such as Sp. santonensis d'Orbigny, 1847 (from the Coniacian-Santonian of Aquitaine), Sp. truncatus (Lamarck, 1819) (from the ConiacianSantonian near Tours, Loire valley), Sp. spinosus (J. Sowerby, 1814) (from the Cenomanian-Maastrichtian of the European chalks), Sp. fornii Greco, 1917 [from the (?) Maastrichtian of Egypt], Sp. likhatschevi Bobkova, 1961 and Sp. baIakhanensis Bobkova, 1961 (from the Turonian of the Tadzhik depression, Tadzhikstan) all have either strongly developed spines, or a different rib development, and/or a free life position throughout most of their adult life. Distribution: Only known from rudist limestones: uppermost Coniacian-Iowermost Campanian of Lago di S. Croce, eastern Venetian Prealps, and Santonian-Lower Campanian of Val Meduna (Friuli, NE Italy) and of Capo di S. Maria di Leuca (Apulia, southern Italy).»
[1] Futterer (op. cit., p. 33) mentions a Spondylus sp. from rudist beds outcropping to the east of Lago di S. Croce (= Pinei?). This specimen is housed in the collections of the Naturkunde Museum in Berlin: it has all the characteristics of a neitheinid.
DHONDT, A. V. & I. DIENI. 1993. Non-rudistid bivalves from Late Cretaceous rudist limestones of NE Italy (Col di Schiosi and Lago di S. Croce areas). Memorie di Scienze Geologiche, 43: 165-241, pls. 1-20, text-figs. 1-18. [p. 202, 204]
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Spondylus arcuatus (Catullo, 1834); A. Dhondt & I. Dieni, 1993, Non-rudistid bivalves from Late Cretaceous rudist limestones of NE Italy (Col di Schiosi and Lago di S. Croce areas), plate 10, figures 1-4; plate 11, figures 1-5; plate 12, figures 1-9; plate 13, figure 16.
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