New Species of Paleozoic Fossils. 183 



beak incurved. Yentral valve marked by a moderate mesial depres- 

 sion, and by four or five subangular plications on each side, the 

 s'econd on each side the mesial fold not extending to the beak, but 

 having their origin at a lower point. Cardinal area proportionally 

 high, undefined at the sides, but gradually rounding into the general 

 surface of the valve; higher than wide. 



Surface marked by fine, distinct, straight thread-like strife, which, 

 in the perfect condition, are crenulated by concentric striae. 



This species bears considerable resemblance to S. Tiro Barr. from 

 the Silurian of Bohemia, but differs in the projection of the beak, 

 and in the radiating stri^ of the surface. Among the American 

 Silurian forms it approaches S. Eudora Hall, most nearly, but is 

 not so vcntricose, and has a more projecting beak and fewer 

 plications. 



Formation and locality. In limestone of the age of the Niagara 

 group, at Louisville, Ky. From the cabinet of Dr. James Knapp. 



Spikifeka (Ctktia) tkapezoidalis. 



Spirifera {Cyrtia) exporrecta Wahlenberg, and S. trapezoidalis 

 Hisinger, are identical according to Davidson. 



A specimen, having the form and all the characters of the larger 

 European forms of this species, occurs in the collection of Dr. Knapp. 

 Another one, with much greater elevation of the ventral valve, var. 

 arrecta, appears in the same association. 



PeNTAMEKUS OBLOiq"GUS SoW. 



This species occurs near Louisville, in strata of the age of the 

 Niagara group of New York. 



A single specimen examined has the aspect and proportions of 

 those from Eochester and other places in New York, but has a length 

 of only one inch and a half. The messial lobe is well defined, and 

 there is an indication of a sinus on each side, giving the incipient 

 condition of the trilobate form of P. trisinuatus McOhesney, which 

 occurs more commonly in the northwest. 



Another form of Pentamerus which we regard as of this species, 

 var. cylindrical occurs in the same locality ; the shell has a length of 

 two and a lialf to three inches. The beak of the ventral valve is 

 often considerably extended, acute and incurved. The body of the 

 shell usually preserves some faint indication of the prevailing lobed 

 character of the species. 



In this phase the fossil resembles the Amj)higenia {Pentamerus) 

 elongata of Yanuxem, but it is not so broad and gibbous in the upper 

 part of the shell, and the valves are not usually i jpressed in front, 

 as in that species. 



Notwithstanding the wide deviation sometimes observed in these 



