TRENTON LIMESTONE. 137 



ATRYPJS 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 Leptjena 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 ATRVPiE 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, 



Pi-. XXXIII. Figs. 1 a, b. 



Atrypa extaru, Conrad in MS. Emmons, Geol. Report, 1842, pag. 395, fig. 6. 

 Compare Atrypa sublobata, Portlocs., Geol. Tyrone, &c. 1843, pag. 567, pi. 38, fig. 2 b and ft. 

 — undata. Sowebbt, Sil. System, 1839, 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. 1 b; 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 striee. 



Length and breadth varying from f to J 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 

 pedinella, tfc. 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, btit simple elevated striae, more 

 prominent than the fine longitudinal striee that usually appear towards the margin. 



Fig. I 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 



