80 A. E. Verrill — Study of the family Pectinidce. 



one to three larger, and numerous smaller tentacles. The latter dif- 

 fer greatly in size ; the outer ones are small, very numerous, and 

 much crowded. The guard-tentacles (fig. 8a) are shorter, conical, 

 and alternate in two or more rows. 



This large species occurs abundantly in many localities off the 

 coast of the United States, north of Cape Hatteras, from just below 

 low-water mark to 60 fathoms, and is sometimes taken below 100 

 fathoms. It is used as an article of food to a considerable extent in 

 New England. 



Hyalopecten dilectus Verrill and Bush, sp. nov. 



Shell small, thin, fragile, strongly undulated, slightly oblique, with 

 the ventral margin broadly rounded ; dorsal margin straight. 



In the right valve, the anterior auricle is elongated, with a deep 

 angular notch beneath ; the posterior auricle is shorter, with a 

 prominent dorsal angle, which is less than a right angle, owing to 

 the emargination of the posterior end ; in the left valve the anterior 

 auricle is broad, with its posterior angle nearly rectilinear, and it 

 forms a right angle with the dorsal margin ; the posterior end has a 

 slightly prominent angle and a posterior emargination in both valves. 

 The anterior auricle is marked by several fine, rough, radial ridges, 

 which are more numerous and stronger on the left valve. The beaks 

 are a little prominent and project somewhat above the dorsal margin. 



The surface of both valves is covered with broad and rather regu- 

 lar undulations, most prominent on the left valve ; the undulations 

 are crossed by regular, well-spaced, thin, raised radial lines, becom- 

 ing finer and more crowded at the ends of the shell ; they are nearly, 

 obsolete in the right valve, being indicated only by microscopic striae. 



The interior is strongly undulated and marked by very distinct 

 radial grooves in the left valve, and by faint ones in the right valve. 

 Resilium small, central ; color, dirty white. 



Length, 8™™ ; height, the same. 



One living specimen (No. 52,539), from station 2570, off Martha's 

 Vineyard, in 1813 fathoms, 1885. 



This species is figured in an article bj^ Verrill and Bush, sent to 

 the Proceedings of the U. S. National Museum, several months ago, 

 but not yet published. 



It is closely allied to P. fragilis of Jeffreys, and resembles pretty 

 nearly his figure (Proceedings Zoological Society of London, plate 

 45, figure 1), which probably represents a species distinct from the 

 original type described by him. It may be identical with our shell. 



