TRENTON LIMESTONE. 137 



ATRYI'yE OF THE TllENTON LIMESTONE. 



Several species of this gemis arc widely clifTiised in tlie Trenton limestone, tliong-h none 

 of tlicni are so abundant in New-York as the Lkptjena and Ortiiis. The species most 

 common in this Stale 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 tiie LEPTiENA, and the Orthis testudinaria., occur at nearly every localitj' of tlic 

 Trenton limestone in New-York, the AtrypjE are for the most part restricted, and the 

 dilTerent species can only be sought successfully at dillerent 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 paleonto- 

 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 extant!, Conr.vd in MS. Emmons, Geol. Report, 1842, pag. 3'J5, fig. 6. 

 Compare Atrypa subtobata, Portlock, Geol. Tyrone, &c. 1S43, pag. 567, pi. 3S, fig. 2 b and k. 

 — undata. Sowerby, Sil. System, 1S39, pag. 637, pi, 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. li; beaks 

 very small ; dorsal valve transversely oval, with a broad, deejj, not angular mesial sinus, 

 defined by subangular margins ; ventral vulve 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 | of an inch. 



This shell is somewhat common at one or two localities about Watertown in Jeflerson 

 county, in a grey subcrystalline limestone, associated with Trochus Icnticularis, Orthis 

 pectinella, Sfc. It is remarkable for the extended cardinal line, wliicli 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 stria, more 

 prominent than the fine longitudinal strife that usually appear towaids 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.) 

 [ Paljjontologv.] 18 



