A. E. Verrlll — Study of the family Pectinidce. 87 



prominent ; the beak is less acute and scarcely projects beyond, and 

 often falls short of the hinge-margin, but the inequality is less 

 marked than in most of the allied species. 



Length of one of the largest specimens 7"°™ ; height 6'"™ ; dorsal 

 hinge-margin 4™™. 



It was taken in considerable numbers. It is so distinct from all 

 the other species of our coast that a detailed comparison is unneces- 

 sary. 



Off the eastern coast of the U. States, opposite Chesapeake Bay 

 and Cape Hatteras, in 43 to 132 fathoms. Although very small, 

 this species seems to be adult. 



Cyclopecten simplex Verrill, sp. nov, 



Plate XVI. fig. 1 : Plate XIX. figs. 1, 2. 



Shell well rounded, thin, compi'essed, hyaline. Auricles large, 

 prominent at both ends, unequal, in the right valve the anterior end 

 is considerably prolonged, with a deep byssal notch, and the poste- 

 rior end is less prolonged with a rather deep emargination or sinus ; 

 in the left valve both ends are shorter and angulated. The left valve 

 is nearly smooth ; the right valve is covered with fine, crowded, 

 concentric, incised lines, and has faint radii on the anterior auricle. 

 Resilial pit small. Transverse incisions of the hinge are fine and 

 vermiculated or irregular. 



Height, 4*4"''" ; breadth about the same. West Indies, U. S. Fish 

 Com. 



Propeamusium thalassiuum (Dall) Verrill. 



Pecten fenestratus Verrill, Proc. U. States Nat. Mus., iii, p 403, 1881 {non Forbes). 

 Amusiuni fenestratum Verrill, these Trans., v, p. 582, 1882. 



Pecten {Pseudamusium) thalassinus Dall, Bulletin Mus. Comp. Zool., Blake Exp., 

 Pelecypoda, vol. xii, p. 221, 1886. 



Plate XIX. figs. S-T. 



This species has been very well described by Dr. DalP, but has 

 not been figured. 



The larger specimens and some of the young not more than 4 or 

 gmm jj^ diameter have an internal, raised, opaque white, radial rib, on 

 each end, below the auricles, within the concavity of the shell, and a 



^Dr. Dall, in the work quoted, has called the upper valve the right and the lower 

 valve the loft, and consequently has reversed the anterior and posterior ends, in the 

 descriptions of this and several other species of Pectinidfe. He informs me that this 

 was done inadvertently, and should be corrected. 



