914 PALEONTOLOGY OF NEW-YORK. 



where the surface is partially or entirely exfoliated, the bifurcating cha- 

 racter of the striae is not observed ; and in one specimen, they appear 

 to have been nearly simple throughout. 



The plications are crossed by fine imbricating lamellose striae, which 

 are abruptly arched backwards. 



A cast of the ventral valve shows a large oval muscular area, which 

 is deeply divided by a rounded median crest, and strongly striated on 

 the lateral portions. 



After exaiiiiuing all the collections that have been made, I am unable to point 

 out any specific diflference between the specimens originally described by me as 

 S- divancatus, and those subsequently described as 8. venustus, from the Hamil- 

 ton group. The specimens then before me were in the condition of the one figured 

 on plate 32 figure 1 ; while the Hamilton specimens, illustrated in figures 2-6, 

 offered at first view very little similarity with those of the limestone, and were 

 regarded as a distinct species. Other specimens from the limestone have a neai-er 

 approach to those of the Hamilton shales. 



This shell, in its proper form and proportions, is one of the finest Spirifers in 

 the whole series, and is readily distinguished from all others by the bifurcating 

 plications and sharp zigzag concentric strise. The largest specimen geen has a 

 width of nearly three inches with a length of two inches, and a depth of one inch 

 and an eighth. 



Geological formations and localities. In the Comifcrous limestone at Scho- 

 harie; at Stafford in Genesee county; at Williamsville and Clarence in Erie 

 county. In the Hamilton group, at York, Livingston county. I have seen a frag- 

 ment of this species from the limestone near Port Colbornc, Canada West. 



Spirifera fimbriata. 



PLATE XXXIII. 



Dtlthyrit fimbriata : Cohbad, Jour. Acad. Nat. Sciences Philadelphia, Vol. viii, p. 268. 1842. 

 Spirifer fimbriata ; Conead ; Biilinos in Canadian Journal, p. 259. 1861. 



Shell transversely subelliptical, gibbous : hinge-line less than the width 

 of the shell ; cardinal extremities rounded. 



Ventral valve gibbous in the upper half, regularly curving to the front 

 and sides ; sinus well defined, usually shallow and rounded, sometimes 

 deep and angular, and much produced in front ; beak small and 

 incurved over the area, which is high and concave and extending 



