MOLLUSCA. 617 



Genus PE'RONAEODERMA Poli. 



Peronaeoderma georgiana Gabb. 



Plate LXX., Figs. 4-6. 



1876. Peronccoderma Georgiana Gabb., Proc. Acad. Nat. Sci. 



Phil. (1876), p. 308. 

 1905. Peronceodernm georgiana Johns., Proc. Acad. Nat. Sci. 



Phil. (1905), p. 1 6. 



Description. The dimensions of a small specimen are : length, 

 24 mm.; height, 14.5 mm. Shell broadly subtriangular in out- 

 line, nearly equilateral, the beak nearly central in position. An- 

 terior and posterior cardinal margins sloping nearly symmetri- 

 cally, meeting at the beak in an angle of about 133; anterior 

 and posterior margins both sharply rounded and nearly sym- 

 metrical, the greatest extension considerably below the middle of 

 the shell; the posterior margin sometimes appearing to be ob- 

 liquely subtruncate above; basal margin gently convex through- 

 out, curving upward a little more strongly in front and behind. 

 Valves depressed convex, most prominent between the beaks and 

 the center of the shell, the surface curving somewhat abruptly to 

 the cardinal margins, very gently to the anterior, posterior and 

 ventral margins. Upon the post-cardinal slope just within the 

 cardinal margin and subparallel with it, is a narrow and shallow 

 sinus which has a slight downward curvature posteriorly and 

 becomes extinct before reaching the posterior margin. Surface 

 of the shell marked by regular, concentric lines, two or three of 

 which occupy the space of one millimeter. 



Remarks. This species occurs abundantly in the Wenonah 

 sand near Marlboro, and these specimens have been compared 

 carefully with Gabb's types of the species in the collection of the 

 Philadelphia Academy of Science. The specimens from the two 

 regions agree as closely as can be expected in the case of speci- 

 mens so differently preserved, and the specific identity of the 

 northern and southern forms can be assumed with certainty. 

 There seems to be no essential generic difference between this 

 species and the one which has been referred to Tellin-a georgiana, 



