144 PROCEEDINGS OF THE ACADEMY OF 



The above two species are interesting additions to a genus which has 

 hitherto been quite limited in species. The discovery of two (possibly three) 

 new species of Pholadacea inhabiting the West Coast of North America, occur- 

 ring within a few months, proves the truth of the remarks I made on this subject 

 in the Proc. A. N. S., 1862, that, " greatly as the number of species have been 

 increased by modern research, it is evident, from the general diffusion of the 

 Order throughout the world, and from the incompleteness of our researches in 

 those regions, which appear most to abound in them, . . . that the number at 

 present known must be indeed a very small proportion of those which future 

 investigation will probably reveal to us." 



ZiEPHiEA Gabbii, Tryon, plate 1, fig. 1. 



Shell large, transverse, obliquely divided by a deep furrow proceeding from 

 the umbonal apex to the basal margin and forming a corresponding rib on the 

 internal surface of the valve. Posteriorly to the furrow the shell is marked 

 only by growth lines which, in crossing it, are elevated into sharp ribs, in which 

 character they are continued to the anterior margin. The portion of the shell 

 anterior to the radiating furrow is ornamented with numerous longitudinal ribs, 

 approximating in pairs and rendered acutely scabrous at the intersection of 

 the rib- like growth lines. 



Ventral anterior margin emarginate. Dorsal anterior margin reflected and 

 closely appressed over the beaks. Posterior dorsal margin declining somewhat 

 to the quadrately rounded posterior lateral end. Color white. 



Dimensions. Length \\ inch ; breadth 2j inch. Breadth anterior to furrow 

 9-10 inch ; posterior to furrow 1 J inch. 



Hab.~ Coast of Japan ? W. M. Gabb. My cabinet. 



Observations. This species is very closely allied to Z. crispata of our Atlantic 

 coast, but may be distinguished by its more numerous and more scabrous ribs, 

 by its greater proportionate width and the very disproportionate size of its an- 

 terior and posterior areas. 



Can this be the species which Dr. Carpenter, in his Catalogue of our West 

 Coast Mollusca, refers with doubt to Z. crispata? In the exchanges of com- 

 merce it may have been brought there, or, (no strange distribution in this 

 family) it may even exist on both shores of the Pacific. 



I received a single valve, somewhat mutilated, from our fellow member, Mr. Wm. 

 M. Gabb, now of San Francisco, Cal., and name it after him, in recognition of 

 the active service he is rendering to the science of Conchology in his adopted 

 State. 



Xylotrta setacea, Tryon, plate 1, fig. 2, 3. 



Shell large, of nearly equal length and breadth. Beaks high, narrow, in- 

 curved, and thickened, the apex lower than the auricle, which is long, moderately 

 wide, extending more than half the length of the valve and joining the medial 

 portion by a rounded obtuse angle. Anterior area obliquely triangular, not more 

 than half the length of the auricle, its upper edge protected by a rib culmina- 

 ting dorsally in a sort of knob. The anterior margin of the medial portion of 

 the valve is straight, forming an acute angle with the triangular area; the 

 posterior margin is oblique and somewhat convex. The junction of the auricle 

 is marked externally by a depression of the surface, and internally by a pro- 

 jecting ledge. Apophysis short, oblique, broad. Base of valve tuberculate 

 internally. 



The valve is white, tinged with pink anteriorly and slightly glossy. The 

 anterior area, which is separated from the body by a deep, narrow, sulcation, is 

 sculptured by about thirty sharply cut, prominent, transverse ribs. The body 

 is marked, first, by a narrow longitudinal area which is closely striate; then by 

 a narrow double rounded rib, the surface of which is triangularly striate; then 

 by a depressed space equally wide, with its sides accurately defined, and trans- 

 versely sculptured. The whole surface of the body and auricle posteriorly is 



[May, 



