290 PALAEONTOLOGY OF NEW YORK. 



septum in these Devonian and Carboniferous terebratuloids gives a greater sim- 

 plicity to the variations of the loop in different st<ages of growth, though 

 their final condition is the same. 



Cryptonella ranges upward into the early faunas of the Carboniferous period ; 

 well defined internal casts of a large form like the full-grown examples of 

 C. planirostra, occur in the Waverly group of Ohio, and it seems probable that 

 the Centronella Alii, A. Winchell, described from the Marshall group of Michigan, 

 will prove to be a Cryptonella. 



Accompanying precisely the same structure of hinge-plate as that just 

 described is a variation in the form of the brachidium presented by several of 

 the Devonian species which have usually been referred to Terebbatula, namely, 

 T. Suilivanti, T. Harmonia, Hall, of the Corniferous limestone, T. simulator and 

 T, Lincklani, Hall, of the Hamilton group. The " brachidium, compared with 

 that of the normal Cryptonella, is quite short, extending less than one-half the 

 length of the brachial valve, and the recurvature of the ascending branches 

 exceedingly slight. This recurved lamella is so delicate that it is rarely 

 completely preserved, but when retained the entire brachidium has the form 

 represented in the adjoining figure. The crural apophyses are situated more 



FlO. 209. FlO. 210. 



Fig. SOB. Terebratula {Eunella) limulator. Hall; showing the character of the hinge-plate, the relative length and 



usual preservation oT the brachidium, with the ascending band lost. 

 Fig. 310. TarOiratulaHEvneUa) SulUcanti, Hall; a dorsal view of the complete brachidium. 



anteriorly than in Cryptonella and are much broader at the base. It would 

 be hardly justifiable to include these species in the same group with typical 

 forms of Cryptonella, and hence, to forms having this type of brachidium, it 

 is proposed to apply the term Eunella. 



