434 
PALAEONTOLOGY OF NEW-YORK. 
Genus Renssemeria* (Hall). 
Tcrebratula : Eaton, 1834 — 1842. 
Atnjpa : Conrad, 1839. 
Pentamerus : Vanuxem, Hall, 1843. 
Atnjpa : Yanuxem, Mather, Hall, 1843. 
Meganteris : Hall, 1856 & 1857. 
Rensselaria : Hall, 1858. 
Generic Description. Shell inequivalved, oval, ovoid or suborbicular, 
elongated or rarely transverse and sometimes subtriangular, generally 
gibbous or ventricose. Valves more or less convex, without mesial fold 
or sinus : beak prominent, acute, more or less incurved; foramen 
terminal, sometimes concealed, round or oval, the lower side formed 
by two small deltidial pieces, and, in their absence, by the umbo of the 
opposite valve, and then appears triangular. Shell structure distinctly 
punctate. 
Surface radiatingly striated or finely plicated, rarely smooth? 
Valves articulating by two somewhat widely separated teeth in the 
ventral valve, with corresponding sockets in the dorsal valve. The 
diverging cardinal teeth supported by strong dental plates, which, on 
their anterior margins, extend about half the depth of the cavity of 
the valve, when they turn abruptly towards the beak, and approach 
each other or unite in the rostral cavity : from this point of return, 
there is a low ridge bounding the muscular area, which is an elongate 
more or less oval depression, in the centre of which the adductor 
muscles occupy two small narrow scars; a more or less prominent 
median septum extends the entire length. 
In the dorsal valve, the dental sockets lie between the shell proper, 
and a strong, often much thickened process, from the anterior extension 
of which proceed the slender crural processes, first in a direct line, and 
* I have given this generic designation to commemorate the name of the late Hon. Stephen Van Rens¬ 
selaer, to whose munificence we owe the early geological and agricultural surveys in the State of New- 
York; and to whose liberality, in establishing the Rensselaer School for teaching the sciences with then- 
application to agriculture and the arts, I conceive is due the great impulse given to the study of the natural 
sciences, at a period when these pursuits were little fostered in any of our institutions of learning; and if 
the results of the Geological Survey in New-York are entitled to any pre-eminence, we arc indebted to this 
early influence more than to any other cause. 
