166 PALEONTOLOGY OF NEW JBESEY. 



quite regularly transversely ovate, widest across the anterior end, Avith 

 very small, appressed beaks, but slightly rising above the hinge margin 

 and almost centrally situated. Valves very depressed convex. Surface of 

 the shell marked by rather fine, regularly increasing, concentric ridges, 

 which are elevated, and separated by sharply depressed spaces of nearly 

 equal width. These are crossed by radiating ridges, which are strongest 

 for a short distance from the anterior end and on the postero-cardinal slope, 

 being sharp and coarse on the latter part, but broad and gently rounded on 

 the anterior end; while on the middle of the valve they are much finer 

 and very subdued, scarcely appearing except in the depressions between 

 the concentric ridges, and barely observable without the aid of a glass. 



This shell seems to have been Mr. Conrad's type of the genus 

 Linearia, as far as the structure of the hinge is to be considered, the characters 

 of which he appears to have obtained from the Haddonfield specimens; 

 while the species was first described from examples of small size, from 

 Snow Hill, N. C. The hinge-plate, as shown in the New Jersey shells, is 

 rather wide, the cardinal teeth are seen to be two, narrow, oblique, and 

 slightl)^ diverging, directed anteriorly, the posterior of the two strongest 

 and rather rounded on the back in the right valve, with a long, shallow but 

 distinct pit distant from the beak on each side, representing the laterals of 

 the left valve. The muscular impressions are large and shallow, while the 

 pallial line is invisible on any of the specimens which I have examined; 

 but Mr. Conrad says "the pallial sinus is rounded and extends to a direct 

 line between the apex and ventral margin, according to D'Orbigney's fig. 5, 

 and beyond that point in fig. 17," referring to some one of D'Orbigney's 

 works which he does not cite. In the specimen, of which I liave figured the 

 interior, the pallial line is entirely covered with a paper pasted over the 

 inside of the shell, to hold together the many fragments into which it has 

 been broken, so that I dare not attempt its removal. 



Formation and localities. — The larger cast figured is from Holmdel, 

 New Jersey, in a collection made by the Rev. Dr. Riley. The shells are 

 from Haddonfield, and Conrad's type of the species was from Snow Hill, 

 North Carolina. 



