Caribachlamys guayubinensis Waller, 2011
WALLER, T. R. 2011. Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae (Mollusca: Bivalvia: Pectinoidea) of the Cibao Valley. Bulletins of American Paleontology, 381: 1-197, pls. 1-18. [p. 27, pl. 2, figs. 6-9]
2011 Caribachlamys guayubinensis Waller, 2011
T. R. Waller, 2011, plate 2.
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«Diagnosis.— Caribachlamys with 30 or fewer ribs at 30 mm Ht, without clear clustering of ribs on RV or ordering on LV; scales on ribs open and concave on their ventral sides, not closed and knobby.
Description.— Shell reaching ca. 45 mm Ht, height exceeding length, umbonal angle narrow, ranging from ca. 83° in submature specimens to somewhat over 90° in largest specimens, acline to slightly prosocline, convexity moderate with RV slightly more convex than LV, disk gapes absent. Disks with radial ribs originating < 1 mm from beak on LV, increasing in number throughout ontogeny by branching on sides of ribs on RV and by intercalation near edges of rib interspaces on LV, 16-19 ribs at 5 mm Ht, 23-30 mm by 30 mm Ht, with higher numbers at greater shell heights; primary ribs equal to or narrower than interspaces, with rounded crests and steep sides; all ribs bearing wide, strongly projecting, distally inclined, distally concave scales. Antimarginal or diagonal microstructure in interspaces in early ontogeny; commarginal lamellae weakly developed in early ontogeny, absent later. Disk flanks moderately high and rounded on LV, much steeper or even slightly inturned on RV, commonly lacking radial costellae. Auricles very unequal, anterior slightly more than twice length of posterior; right anterior auricle with 4 or 5 strong scabrous radial costae, broad byssal fasciole, deep byssal notch, and active ctenolium; left anterior auricle with anterior margin concave ventrally, slightly convex dorsally, with overall trend forming acute angle of 60º with dorsal margin, with 3 or 4 moderately strong, scabrous radial costae in dorsal half, fainter costae in ventral half; posterior auricles with posterior margin nearly straight in ventral part, becoming slightly concave in dorsal part before intersecting dorsal margin, overall trend of margin forming obtuse angle of ca. 134º with dorsal margin, surface with 4 or 5 costae of uneven strength, strongest along dorsal margin; total hl slightly greater than ½ L. Hinge dentition as in Chlamys, with moderately strong dorsal and infradorsal teeth and weak resilial teeth. Ribs on interior of shell lacking carinate edges near shell margin. Muscle scars and extent of foliated-calcite re-entry on shell interior not accessible or not preserved. Etymology.— Named after the town of Guayubín, Province of Monte Christi, northern Dominican Republic. Type material.— Holotype, USNM 540944, 1 LV, 38 mm Ht (restored), 34.0 mm L (Pl. 2, Fig. 7). Type locality.— TU 1438, Mao Adentro Limestone Member?, Mao Formation, road cut 0.5 km south of bridge at Guayubín, on road to Sabaneta, northern Dominican Republic. Other material.— Paratypes: 3 RV, 2 LV, from the type locality, TU 1438; TU 1281, one partial LV; TU 1245, one partial LV, all from the "Mao Adentro Limestone" in the Guayubín area. Remarks.— All of the specimens of Caribachlamys guayubinensis n. sp. are associated with a somewhat chalky, white, bioclastic limestone showing evidence of dissolution of aragonitic components, including branching corals. It is unclear whether the limestones exposed at the northwestern end of the Samba (or Zamba) Hills in the vicinity of Guayubín (localities TU 1245, 1281, 1438) should be assigned to the Mao Adentro Limestone, the type locality for which is on the Río Mao (Vaughan in Vaughan et al., 1921: 73). H. Vokes (1989: 123), referring to these limestones at locality TU 1281 near Guayubín, remarked that they represent a "back-reef and/or lagoonal facies" and that although their assignment to the Mao Adentro Limestone is debatable, they are "the source of the material in the Mal Adentro gravity flows," that is the true Mao Adentro Limestone on the Río Mao. Saunders et al. (1986: 38) emphasized that they had no direct evidence for the age of the true Mao Adentro Limestone. The presence in the Guayubín area of three species, Caribachlamys guayubinensis n. sp., Mimachlamys vokesorum n. sp., and Argopecten ameleus, that are unknown in other shallow-water facies of the Cibao Valley suggests that the Guayubín limestones are younger than these other facies. This is supported by the occurrence of A. ameleus, a species described from the Bowden Formation (Bowden shell bed) of Jamaica, which is now regarded as late Middle Pliocene in age (Kohl & Robinson, 1998), and by the presence of C. guayubinensis n. sp., the closest relatives of which are Late Pliocene to Recent species. One of the main diagnostic features of the genus Caribachlamys reported by Waller (1993: 217) is the presence of a lecithotrophic-type prodissoconch in which the PI stage is large and the PII stage short or absent. None of the seven specimens of C. guayubinensis n. sp. has the prodissoconch preserved, but these specimens are placed in Caribachlamys based on their rib pattern, scale development, and microsculpture. Comparisons.— Among the known species of Caribachlamys (Waller, 1993), C. guayubinensis n. sp. is closest to C. mildredae (Bayer, 1941), an extant species known from southeastern Florida (Waller, 1993: 225, fi gs 9c-e). Unlike that species, C. guayubinensis n. sp. lacks the clear clustering of ribs on the right valve and multiple ordering of ribs on the left valve and has fewer ribs at a comparable size (25-30 at 30 mm Ht, compared to 35-40 in C. mildredae). Evolution.— The occurrence of Caribachlamys guayubinensis n. sp. within a limited geographic area in limestones that could all be of approximately the same age does not allow recognition of any stratigraphic trends within the Dominican Republic. However, C. guayubinensis n. sp. might be an early member of a clade that contains the extant species C. mildredae and C. imbricata (Gmelin, 1791). These extant species share three characters not found or scarcely developed in C. guayubinensis n. sp.; rib clustering (on right valve), rib ordering (on left valve), and a tendency to develop knobby closed scales, the last feature being well developed in C. imbricata. Occurrence and distribution.— Known only from the "Mao Adentro Limestone" of the Guayubín area, northern Dominican Republic.» THOMAS R. WALLER, 2011
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