48 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



It is not probable that materials for other genera, or for reference to 

 established genera, are yet exhausted among the TerebratuliDuE of the 

 Upper Silurian and Devonian rocks. While engaged in these investiga- 

 tions, Dr. C. RoMiNGER has kindly sent to me a fossil from the Hamilton 

 shale of Thunder bay (Michigan), in which the terebratuloid loop is dis- 

 tinctly visible. The form of the shell is ovate, not very unlike Cryptonella 

 ( = Centronella), but more rotund, the lateral edges more incurved, and 

 the space below the beak of the ventral valve not so great, nor the deltidial 

 plates so conspicuous as in species of that genus. On a critical examination 

 of the interior, after cutting away the crystalline filling of the shell nearly 

 to the loop, I am unable to find any difi'erence between it and true Tere- 

 BRATULA ; and we have, so far as I know, for the first time the positive 

 determination of this genus in our Devonian rocks. The position and pro- 

 portions of the loop are shown in fig. 22, which is an outline of the shell 

 from the dorsal side, twice enlarged. Fig. 23 is an enlargement of the loop, 

 showing the crural process. 



Fia. 22. ■ Fig. 23. 



Figs. 22 & 23. Illustrations of Terehratula romingeri (Winchell). 



At the same time. Dr. Kominger has also sent me specimens of Terc 

 hratula melonica of Barrande, one of which he has prepared so as to 

 show in a very satisfactory manner the loop in its entire extent. The speci- 

 mens correspond with those I have received from M. de Verneuil under 

 the same name, and therefore we must regard them as authentic. The ex- 

 ternal form of T. melonica is not unlike some of the less gibbous forms of 

 Cryptonella, and is much less gibbous than the usual forms of Wald- 

 HEIMIA. The lamellae are nearly parallel and near together, and the loop 

 is extended four-fifths the entire length of the shell ; when it is recurved, 

 and, turning back, extends two-thirds of the distance to the beak of the 

 dorsal valve. The crural processes are farther from the base of the loop than 

 is represented in the typical figures of Waldheimia, and are opposite the 

 recurved extremity of the loop. 



The accompanying figures illustrate all that has been observed in this 

 species. 



