﻿302 lM,AGI()l.y\ 



Walker. This si)C'cics lias not tlic female form of castanciis, 

 and the dorsal scars are in the bottom of the 1)eaks in jilace of 

 heing^ on the teeth. 



In outline it is nearly the same as ['. strodccDiits I'.. II. W'r. 

 hut differs in heinjj: i^reenish, w hile strodcainis is dead black . 

 its beak cavities are deeper, and its teeth are much, longer, 

 stouter and more erect. 



From U. ciirtiis. to which it is allied, it differs, lacking- the 

 pronounced swelling- before. 



Many of these shells show a constriction like the U. con- 

 strictns of Conrad, and it mav be that this is a sexual mark." 



The followiui;- species are unfi^ured or indeterminable. 

 Ohoi'aria cordata l\.\i-MNESQinv, Ann. Cen. Sci. lirux.. \'. 1820, 



p. 312, pi. I. XXXI I, fis^^s. 6, 7. 

 Oho7aria stegaHa K.\i'iKKS(jv\:, Ann. den. Sci. Unix.. \'. 1820, 



p. 312. pi. Lxxxii, figs. 4, 5. 

 Olwvaria striata Rafixesoi'E, .Vnn. Gen. Sci. T.rux.. \'. 1820. 



]). 311. 

 Obovaria torsa R.\FiNnsorE. Ann. Gen. Sci. TVux.. \', 1820, 



p. 312. pi. Exxxii. figs. 1. 3. 

 Obliqiiaria rctnsa Raeinesoue. Ann. Gen Sci. Rrux.. A\ 1820. 



p. 306. pi. I, XXXI, figs. TO. 20. 



Genus PL.AGTOL.\ ( Rafines(|ue. t8io) .-Xgassiz. 



riagiola R.vFiNESoiTE, J. de Phys. Cliini. Hist. Xat., 1819. p. 

 426. — Agassiz, Arch, fiir Nat., 1852, p. 48, redefined. — 

 Ortmanx. Ann. Car. Mus., VIU, 1012, p. 320. 

 Shell triangular ovate, somewhat inflated, solid, with a dis- 

 tinct and often sharp posterior ridge ; surface concentrically 

 sculptured ; umbonal area somewhat flattened ; beaks high but 

 compressed, sculptured with delicate, parallel, doubly-looped 

 ridges, the anterior loop rounded, the posterior angular : pseu- 

 docardinals ragged ; laterals club-shaped, straight or slightly 

 curved ; cavitv of the beaks moderate, often somewhat com- 

 pressed : nacre silvery : female shell more or less inflated at 

 post-basal region. 



