TRENTON LIMESTONE. 
137 
A TR YPJE OF THE TRENTON LIMESTONE. 
Several species of this genus are widely diffused in the Trenton limestone, though none 
of them are so abundant in New-York as the LeptaEna and Orthis. The species most 
common in this State are known to occur in Ohio, Indiana and Kentucky, in the same 
formation, and ranging throughout a much greater .thickness of strata. While several 
species of the Lept^na, and the Orthis testudinaria , occur at nearly every locality of the 
Trenton limestone in New-York, the Atrypje are for the most part restricted, and the 
different species can only be sought successfully at different localities. It should be observed, 
however, that many of our most prolific localities of fossils have been but partially explored, 
and therefore we cannot speak with certainty of all ; still it is believed that the palaeonto¬ 
logist will find the above remarks generally true in relation to the distribution of species. 
173. 6. ATRYPA EXTANS* 
Pl. XXXIII. Figs. 1 a, b. 
Atrypa extans, Conrad in MS. Emmons, Geol. Report, 1842, pag. 395, fig. 6. 
Compare Atrypa sublobata, Portlock, Geol. Tyrone, &c. 1843, pag. 567, pl. 38, fig. 2 b and k. 
— undata. Sowerby, Sil. System, 1839, pag. 637, pl. 21, fig. 2. 
General figure somewhat irregularly globose, or subrhomboidal and gibbous, with the 
front produced ; length and breadth nearly equal, measuring the projection of the ventral 
valve ; cardinal line remarkably extended, which is very perceptible in fig. lb; beaks 
very small; dorsal valve transversely oval, with a broad, deep, not angular mesial sinus, 
defined by subangular margins ; ventral valve with a prominent rounded mesial elevation, 
well defined at the margins by a shallow groove ; front produced, and but little elevated 
by the corresponding sinus ; surface marked by concentric somewhat undulating filiform 
lines, and less distinct longitudinal stria:. 
Length and breadth varying from f to f of an inch. 
This shell is somewhat common at one or two localities about Watertown in Jefferson 
county, in a grey subcrystalline limestone, associated with Trochus lenticularis , Orthis 
pectinella, Sfc. It is remarkable for the extended cardinal line, which is more conspicuous 
in the ventral valve ; as also the profound mesial depression and elevation, neither of which 
are angular. The concentric lines are not imbricated, but simple elevated strife, more 
prominent than the fine longitudinal striaj that usually appear towards the margin. 
Fig. 1 a. Dorsal valve, b. Ventral valve. 
Position and locality. Watertown, Jefferson county ; Lowville, and Sugar River near 
Boonville in Lewis county, in the higher portions of the Trenton limestone. 
(State Collection .) 
| Palaeontology.] 
18 
