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. 



a 



4. rt, Cl.lTA.MHDNETKS; 6, GONAMBONITES; C, CLITAJIBONITES; d, OUTHAMIiONITES; «, PLECTAMBONITES. 



After Pander. 



Orthambonites is undoubtedly precisely synonymous with Orthis, Dalinan. 

 Plectambonites is manifestly a good genus, equivalent to Lept^ena 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 ti-iang'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 slojiing from 

 the apex of tlie (-ardinal area, which is generally the highest point, ratlier alii'uptly forward, and more gently 

 toward the sides. Tlie transverse diameter is usually the greatest. 



"The fine longitudinal rilis are interrupted by concentric lines, parallel to one anothei- and to the ante- 

 rior and lateral margins ; thus tlic former lie on one another like steps or roof-tiles. The anterior margin 

 is, in general, straight, rarely, and then but inconsiderably, liending toward the upper valves. As, however, 

 there are gi'eat differences both in c<invexity and in the diameter and height of the cardinal area, it will 

 be more convenient to separate the Klitaud)onites into two divisions, which are distinguished principally by 

 the fact that ill one, which we tiM'iii I'ronites, the upper angle of the triangular cardinal area reaches the 

 highest point in the sh'ell, while in the Hemipronites, the last lies between the posterior and anterior mar- 

 gins, and the cardinal area is therefore lower." 



* Bulletin No. S, U. S. National Museum, p. :!9. 1877. 



