Cyclopecten thalassinus (Dall, 1886)
DALL, W. H. 1886. Report on the Mollusca, Part I. Brachiopoda and Pelecypoda. Reports on the results of dredging, under thesupervision of Alexander Agassiz, in the Gulf of Mexico (1877-78) and in the Caribbean Sea (1879-80), by the U.S. Coast Survey Steamer “Blake”…. Bulletin of the Museum of Comparative Zoology at Harvard University, 12: 171-318, pls. 1-9. [p. 221]
1886 Pecten (Pseudamusium) [sic] thalassinus Dall, 1886
Propeamusium thalassinum (Dall) Verrill; A. E. Verrill, 1897, A study of the family Pectinidae, with a revision of the genera and subgenera, plate 19, figures 5-7.
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«Amussium fenestratum Verrill, Trans. Conn. Acad., V. p. 582, 1882.
Amussium sp. Verrill, Ibid., VI. p. 261, 1884. Left valve less convex and slightly smaller; right valve sculptured much as in reticulus, but less pronounced and without spines, sometimes nearly smooth except near the margin, where traces of the radiating sculpture are always visible; auricles as in reticulus, but less strongly sculptured; left valve with concentric sculpture coarser than in reticulus, notch similar; prismatic structure barely visible on extreme of tbe left valve only; interior of adult marked by a flat thickened margination, especially in the left valve, extending parallel with the basal margin ; auricular crura elevated into u low ridge or blunt tooth on each side ; hinge margin furnished with a lanceolate area on each side of the cartilage pit which is finely deeply closely grooved in a direction vertical to the hinge-line, the projections between the grooves interlocking so strongly as to cause the hinge-line of one valve sometimes to break off bodily, rather than separate from the opposite valve, when one is trying to open a pair, even when the soft parts are absent. The shell is prettily variegated with mottlings of red, brown, and yellow on a creamy ground, both valves participating, but the upper one rather the brighter in most cases. Alt. 8.5; Ion. 9.0; max. diam. 2.0 mm.
This shell has been dredged by Professor Verrill in 80 to 317 fms. off Martha's Vineyard. Specimens were obtained by Sigsbee off Havana in 450 fms., and at Station 36 in 84 fms. The figure on Plate VI. fig. 5. representing the interior of the young fry of Janira hemicyclica, equally well represents the very young of this species, which at this stage can hardly be distinguished from the other except by the external sculpture, which is often absent, or by the rugae of the hinge. Because the internal lira; occasionally fail, or are late in being deposited in certain individuals of Propeamusium, Dr. Jeffreys formed the opinion that they were of no importance as a specific character. In this manner he was led into several errors, from judging merely by the exterior of some of these small shells. In the present case the external sculpture is much like that of Amusium fenestratum Forbes, but finer and more regular. Both have similar varieties of color. Dr. Jeffreys was thus led to unite them, although they belong to different sections of the genus, as also in the case of A. Hoskynsii and Pseudamusium pustulosum Verrill, an error entailing some serious results in the matter of areal distribution. Professor Verrill followed Dr. Jeffreys until a special study of the group enabled me to call his attention to the discrepancies existing between the two species. The peculiar arrangement of grooved and corrugated areas on the hinge-line is of interest in connection with the development of hinge characters. It is very common in the fry of various Pectens. It is well developed in the very young P. magellanicus. I have found traces of it in many of the minute specimens of Pecten I have examined, though often very faint, and in very few does it reach the development attained in the present species. It was the adult and peraianent characteristic of the extinct genus Neithea, and traces of it are even recognizable in some .species of Janira or Pecten in their adult condition. When I first discovered it in the present species, I naturally supposed I had come upon the type of a new generic division, but I have since found it in the young of Pectens of nearly all sections of the genus in its widest sense. On the other hand, in some species even the very young have hardly a trace of it.» WILLIAM HEALEY DALL, 1886
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«Cyclopecten thalassinus (Dall, 1886), an extant species with a broad geographic range in the tropical and temperate western Atlantic and a depth range from 40- >500 m (Abbott, 1974: 449; Theroux & Wigley, 1983), is a close living counterpart of C. almirantensis and differs from C. zalaya n. sp. in the same manner. In addition, C. thalassinus commonly has sculpture of high relief on its left valve.»
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. 24]
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