290 
PALEONTOLOGY OF NEW YORK. 
septum in these Devonian and Carboniferous terebratuloids gives a greater sim¬ 
plicity to the variations of the loop in different stages 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. planirosira, 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 Terebratula, namely, 
T. Sullivanti, T. Harmonia, Hall, of the Corniferous limestone, T. simulator and 
T. Lincklmi, 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 
Fig.'209. Fig. 210. 
Fig. 209. Terebratula (Eunella) simulator, Hall; showing the character of the hinge-plate, the relative length and 
usual preservation of the brachidium, with the ascending band lost. 
Fig. 210. TerebratulaKEunella) Sullivanti, 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. 
