832 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



CYCLOPECTEN Verrill, 1897. 



Cyclopecten VERUILL, Traus. Conn. Aead., X, pp. 70, 90, 92, pi. xvi, fig. 1; pi. 

 xix. figs. 1-4, 1897. 



Types. Cyclopecten pustulosm Verrill and Cyclopecten imbrifer 

 (Lovt'ii). 



Shells thin, rounded, scarcely oblique, with symmetrical auricles and 

 simple margins. The two valves are unlike in sculpture. The right 

 valve is a little flattened and upturned at the flexible margin, so as to 

 fit tightly against the upper valve. The thin lower valve has, in the 

 typical species, regular, thin, elevated, concentric lamella', which aid 

 in the adaptation of the edge to that of the upper valve; the margin is 

 usually flattened or bevelled. The upper (left) valve is radially sculp- 

 tured, rarely smooth; it usually has radial rows of arched scales, 

 pustules, or points, and also concentric raised lines; it is sometimes 

 cancellated. No radial ribs, nor interlocking points at the margin. 

 Auricles well-developed, subequal, angulated and well defined at both 

 ends; byssal notch well-defined; few or no pectinidial teeth, Cardinal 

 folds single, rather feebly developed, often cross-lined. Eyes few. 

 Byssus small, and of few threads. 



This genus includes a large number of small species, mostly from 

 deep-water. 



HYALOPECTEN Verrill, 1897. 



IIyt(lopie)i VERUILL, Trans. Conn. Acad., X, pp. 71,90, 92, pi. xvm, fig. 5, 1897. 



Type. Hyalopectcn undatus Verrill. 



Shell compressed, thin, hyaline. Valves nearly equal, with concen- 

 tric undulations or corrugations, affecting the entire thickness; mar- 

 gins simple; sculpture none, or consisting of fine radial lines on one or 

 both valves, without camptonectes sculpture. Hinge-plate thin and 

 nearly plain; auricles well-developed, unequal; byssal notch distinct. 



For the possible relations of this group to the Mesozoic genus, Syncy- 

 cloncmaj see the original article. 



The species recorded are as follows : H. dllectus Verrill and Bush, 

 from 1,813 fathoms, off Marthas Vineyard; H.fragUia (Jeffreys), from 

 northern Europe and the Arctic Ocean, and off the United States 

 coast, in 578 to 1,525 fathoms; //. undatus Verrill, off the United 

 States coast, in 1,423 fathoms; and H. pudicus (Smith), off Marion 

 Island, in 1,375 fathoms. 



PARAMUSIUM Verrill, 1897. 

 Parain list urn VERRILL, Traus. Conn. Acad., X, pp. 72, 90, 92, 1897. 



Type. Paramusium dalli (Smith). 1 



Shell thin, rounded, much compressed; valves nearly equal; sculp- 

 ture nearly obsolete, different on the two valves; the lower valve with 

 concentric undulations. Auricles very small, equal. Byssal notch and 



'P. dalli ranges from the Gulf of Mexico to Barbados, in 218 to 1,591 fathoms. 



