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. Hamal 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 laraellse, which, after proceeding with a 

 slight upward curye 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 lamellge branch off 

 and converge. 



Fio:. 11. 



Fi2. 12. 



Fig. 11. Hajmal valve oi Siringocephalus Burlini. 



Fig. 12. Profile of shell of same, a, adductor scar; _/, cardinal process ; /), 

 hinge plate ; s, hipmal septum ; vs, neural septum ; ^, dental sockets. 



Type Stringoeephalus 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 o^i 3Iegathyris. 



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? 3Iegathi/ns will show that 

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

 from the outer and hcemal 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 Megathyris are features of the most trivial nature, and 

 analogous instances are found in other species belonging to 

 totally diff'erent genera, for instance Terebratella j)ectunculus, 



