OF CONCHOLOGY. 



113 



in the young ; small and oval in the adult ; deltidium composed 

 of three elements. Neural valve with a pointed apex and a well 

 developed septum. Ili^mal valve with a very prominent cardinal 

 process, forked at the extremity (to receive the edge of the 

 neural septum), provided with a mesial septum. The lower por- 

 tion of the hinge plate supports the crura of the loop in the 

 shape of two flattened lamellas, which, after proceeding with a 

 slight upward curve to near the extremity of the septum, are 

 suddenly reflected and again approach the sockets before sweep- 

 ing submarginally around in the form of a large wide loop, from 

 the inner edge of which a number of smaller lamellee branch off 

 and convercre. 



Ficr. 12. 



Fig. 11. Htemal valve o^ Slringocephalus Burtini. 



Fig. 12. Profile of shell of same, a, adductor scar; y, cardinal process ; p, 

 hinge plate ; s, hjetual septum ; vs, neural septum ; t, dental sockets. 



Type String ocephalus Burtini, Defr., Woodw. Man. Rec. and 

 Foss. Shells p. 222, figs. 130, 131, pi. xv, fig. 13. 



With regard to the position of this genus in the arrangement, 

 I must dissent entirely from the opinion of M. Suess., who places 

 it in the vicinity of Meyatliyris. 



The reflection of the apophyses from the neural edge of the 

 crura (if correctly restored) is a remarkable feature, and the 

 most casual examination of the loop o^ Megatltyris will show that 

 it is totally diff"erent, the reflection in the last named genus being 

 from the outer and licemal side of the crura, as in all the other 

 genera of the TerebratuUdce, which possess a loop. The lamelloe, 

 which have occasionally been noted on the inner edge of the 

 loop of Mcgathyris are features of the most trivial nature, and 

 analogous instances are found in other species belonging to 

 totally difl'erent genera, for instance Terebratella joectunculus^ 



