278 



Report of the State Geologist. 



The brachial valve might easily be mistaken for that of a Spirifer 

 subumbonus, Hall, but the pedicle-valve has all the characteristic features of 

 A. umbonata, varying only in the proportion of height to width. From A. 

 spinosa, Clarke, this variety may prove to differ in the form and proportions 

 of the brachial valve. 



This variety seems to be confined to the Nautilus bed, where it occurs in 

 great abundance. Three very small specimens of this form have however 

 been found in the Strophalosia bed just beneath. These have the sinus in 

 the pedicle- valve shallow and broad, and they also have a distinct depression 

 near the front of the brachial valve. The pits are shorter and more 

 pronounced. Altogether they approach more nearly Spirifer subumbonus 

 though the characters are entirely those of an Amboccelia. 



117o Amboccelia pr^eumbona, Hall. 



1867, Hall, Pal. K Y. vol. 4, p. 262, pi. 44. 



This species is as abundant in the upper two or three feet of the Moscow 

 shales as A. umbonata is in the lower. I have found it as low as four feet 

 below the Styliola band, but it is mainly restricted to the upper portion of 

 the shale. It is abundant in the limestone layer forming the top of the 

 Moscow shales at Section H, where, as in the shale, it is associated with 

 Schizobolus truncatus and Liorhynchus multicostus. A large brachial valve of 

 this species from the upper shale of Section G, measure 18.5 mm. in width by 

 13.5 mm. in height. The species has not been observed below this level. 



118 Amboccelia spinosa, Clarke. 



1894, Clarke, 13th Ann. Rep. State Geol. N. Y. vol. 1, p. 177, pL. 4. 



This species was described from a brachial valve found in the Hamilton 

 shales of the Livonia salt shaft. The long hinge line, the upturned margins 

 of the valve, a low median elevation, and the elongated impressions of strong 

 surface spinules were given as characteristic features. I have found what 

 appears to be this shell, in considerable numbers at Section B, between eight 

 and twenty-three feet below the Encrinal limestone. A few specimens 

 occurred at Section F, in the Moscow shales one and one- half to two and one 

 half feet below the Styliola band. In general appearance these specimens do 

 not differ much from A. umbonata, and this is especially true of the pedicle- 

 valve. The front of this valve appears somewhat more regularly rounded, 

 and the beak slightly more incurved than in ordinary specimens of A. umbon- 

 ata. A large pedicle-valve measures 8 mm. in width with the height about the 



