236 



PALEONTOLOGY OF NEW YORK. 



It was evidently the intention of the author to make not only these two 

 divisions Pronites and Hemipronites of the genus Klitambonites, but also to 

 include as of coequal value the divisions Gonambonites, Orthambonites and 

 Plectambonites ; and the principal differences in these divisions, as based on 

 the varying inclination of the cardinal area, are expressed in the following 

 figures taken from Plate 28 of his work. 



^b 



a 



(i::^ 



FIG. 4. a, Ci-iTAMBONiTES; 6, GoNAjiBOSiTES; 0, Clitambonites; d, Orthambonites; e, Plectambonites. 



After Pandek. 



Orthambonites is undoubtedly precisely synonymous with Orthis, Dalman. 

 Plectambonites is manifestly a good genus, equivalent to Lept^na of authors, 

 not of Dalman. Dall has called attention* to the fact that Pander, in sub- 

 dividing the entire group of Clitambonites, left no type-species upon which the 



shaped, sometimes triang-ular opening- for the passage of the fleshy pedicle. The four sides of the shells 

 are most clearly pronounced; the surfaces are slightly arched, that of the upper valve usually sloping from 

 the apex of the cardinal area, which is generally the highest point, rather abruptly forward, and more gently 

 toward the sides. The transverse diiimeter is usually the greatest. 



"The fine longitudinal ribs are inten-upted by concentric lines, parallel to one another and to the ante- 

 rior and latei'al margins ; thus the foi'mer lie on one another like steps or roof-tiles. The anterior margin 

 is, in general, straight, rarely, and then but inconsidei-ably, bending toward the upper valves. As, however, 

 there are g-reat differences both in convexity and in the diameter and height of the cardinal area, it will 

 be more convenient to separate the Klitambonites into two divisions, which are distinguished principally by 

 the fact that in one, which we term Pi-onites, the upper angle of the ti-iangular cardinal area reaches the 

 highest point in the shell, while in the Hemipronites, the last lies between the posterior and anterior mar- 

 gins, and the cardinal area is therefore lower." 



* Bulletin No. 8, U. S. National Museum, p. 39. 1877. 



