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PALEONTOLOGY OF NEW YORK. 
“ Shell robust, transverse or elongate, sometimes distinctly triangular and 
globose. Valves unequally convex, the dorsal always the deeper. Ventral 
valve with a sinus to which there is not always a corresponding fold on the 
dorsal valve. Hinge-line straight; hinge-teeth very strong, resting on a broad 
hinge-plate. In both valves a small obtusely triangular area, which is higher 
in the ventral than in the dorsal valve. Both valves with a broad pedicle- 
passage, never closed by a pseudodeltidium. Sometimes the beak of the dorsal 
valve is so strongly incurved that its perforation is not visible from outside. 
On the lateral slopes is a more or less strongly defined pseudolunule.* 
“ In the interior of the ventral valve are two long, robust dental lamellae 
which rapidly converge and unite, sometimes before the bottom of the valve is 
reached, then forming a low median septum. Their anterior portion is always 
free while their posterior portions are sometimes coalesced into a single piece. 
In the dorsal valve there are two short crural plates not rising to more than 
one-third the height of the shell; these may remain independent or sometimes 
unite to form a single piece. 
“ The muscles are attached between and on the convergent plates, and, in the 
dorsal valve, also in front of them. 
“ Surface-sculpture more or less finely sieve-like. 
“ Shell-structure apparently fibrous. 
“ All species are confined to the lower Silurian.” 
Type, Porambonites intermedia, Pander.f 
The above diagnosis is that given by Noetling, in an admirable paper on the 
structure and systematic position of the genus.^ Although so old a genus and 
so abundantly represented in the Silurian faunas of Russia, no satisfactory 
conclusion as to its generic affinities had been reached until the publication of 
this author’s investigations, to whose figures of the interior structure of the 
valves, obtained from silicified specimens, the student is referred for illustration 
supplementary to that given in this Volume. 
* This term is applied by Noetling to an area on the cardinal slopes usually delimited by some shai-ply 
defined growth-line of an immature stage of development. It designates a featui'e of slight morphological 
value. 
t Beitrage zur Geognosie des russischen Reiches, p. 95, pi. xvi A, fig. 12. 1830. 
J Beitrag zur systematischen Stellung des Genus Porambonites, Pander; Zeifschrift der deutschen 
geologischen Gesellschaft, vol. xxxv, p. 3.55, pis. xv, xvi. 1883. 
