Grabau — Faunas of the Hamilton Group 



273 



Genus Spirifer, Sowerby. 



105. Spirifer mucroxatus, Conrad. 



1867, Hall, Pal. N. Y., vol. 4. p. 216, pi. 34. 



This is the most abundant species of Spirifer in the Lower shales, being 

 well represented in nearly all the layers below the Encrinal limestone. It 

 appears in the lowest beds into which it passes from the transition shales. 

 In the S. demissa bed and in the shales immediately above, this species is 

 extremely abundant. Throughout those shales specimens occur, showing the 

 mucronate extensions of the hinge line, one of which from the lower beds of 

 the shale measures 15 mm. in height by 100 mm. from tip to tip of the mucronate 

 points. In some of the higher layers, the narrow bulging form appears, 

 which resembles S. consohrinus, D'Orb. In the Encrinal limestone this species 

 is very rare, a few specimens only having been found. These do not show 

 the ordinary characteristics, being in some cases much extended laterallv, 

 without mucronations, and with a number (20 or more) of well marked, 

 rounded plications which are crossed by zigzag concentric lines. The hinge 

 area of these specimens is larger than that of ordinary specimens from the 

 shale, resembling more that of S. consohrinus. Only two specimens of this 

 species have been found in the lower part of the Moscow shale. Its place 

 here seems to be taken by the S. consobrinus which occurs in considerable 

 numbers. Near the top of the Moscow shales a few fragments and casts of 

 this species were found. The prevailing form at this level is S. Ttdlius. 



106. Spirifer Tullius. Hall. 



1867, Hall, Pal. X. Y., vol. 4, p. 218, pi. 35. 



This species is represented by a considerable number of specimens, most 

 of which, however, are small. The species has not been found outside of the 

 Moscow shales, and it appears to be restricted to the upper part of that rock, 

 the specimens found coming from between one and one-half and three feet 

 below the Styliola limestone. They scarcely exceed 8 mm. in width by 5 

 mm. in height, though a few specimens are larger. None, however, approach 

 in size those figured on pi. 35, vol. 4, Pal. N. Y. The plications on each 

 side of the fold and sinus scarcely have the number found in the full- 

 grown specimens. The radiating striations are shown in the majority of the 

 specimens. 



