234 PALEONTOLOGY OF NEW YORK. 



Diagnosis. Shells with a subsemicirciilar marginal outline ; convex or 

 subpyramidal in the typical group. Hinge-line straight, and forming the 

 greatest diameter of the shell. Pedicle-valve elevated, cardinal area high, ver- 

 tical, or sometimes incurved, and crossed by a broad delthyrium, which is 

 normally covered by a convex, perforate deltidium. On the interior of the 

 valve the dental lamelloe are very strongly developed, converging and uniting 

 in the median line before reaching the bottom of the valve ; thus forming a 

 spondylium* which with the deltidium encloses a conical subrostral vault. 

 This plate is supported by a median septum extending for about one-half the 

 length of the valve. Muscular impressions obscure. In the brachial valve, the 

 cardinal area is considerably developed, and the delthyrium filled by a con- 

 spicuous callosity, against the inner side of which the simple orthoid cardinal 

 process abuts. The dental sockets are large, the crural plates low and continu- 

 ous with the edges of the delthyrial callosity. A thickened transverse area is 

 formed in the umbonal region by the union of the inner portions of the crural 

 plates with the cardinal process, and thence a broad median ridge is continued 

 forward through the muscular area, which is sharply defined and quadripartite. 

 External surface covered with radiating striae. Shell-substance impunctate. 



Type, Pronites adscendens, Pander. Lower Silurian. 



American example, Orthisina Verneuili, von Eichwald. Trenton limestone. 



Observations. Although d'Orbigny's term, Orthisina, has found its way 

 into general use for this group of shells, there is no reason why it should replace 

 the name Clitambonites, a genus clearly defined and abundantly illustrated by 

 its author. In order to show Pander's conception of this group, and since his 

 " Beitrage zur Geognosie des russischen Reiches " is a work not generally ac- 

 cessible to American students, his original descriptions and typical figures are 

 here introduced.! 



* liTlovdvXlov , vertebra. This teiin will apply with equal propriety to the similar plate existing in the 

 l)edicle-valvfi of other brachiopods, e. g., Clitambonites, Pentamkrus. Camarella, Stenoschisma, etc. 



t Pander's deterrainations of g-enei'a and species of brachiopoda evince a remarkable insight and ana- 

 lytical power. He was in this i-egard a generation in advance of his contemporaries, who apparently felt it 

 their duty to thi-ow both his g-enera and species back into the old groups whence they were derived, and 

 thus totally ignore his work. The inaccessibility of Pander's works to westc-rn students, has been one great 

 r'ause of the niisnnderstanding of many brachiopodons genera. 



