NOTES ON THE BRITESH JURASSIC BRACHIOPODA. 245 



those of tlie preceding sections bj the presence of a well- 

 defined median sinus in the dorsal valve, which depresses 

 in front the commissure of the valves. 



The beak, which is generally perforated by a small and 

 oblong foramen, is slender, strongly carinated, and hollowed 

 out on the sides. The form of the shell is more or less 

 elongated (13, p. 277). 



Atdacothyris is met with chiefly in the Middle Lias and 

 Inferior Oolite. In the latter division it is well represented 

 by A. carinata, Lam., and its numerous varieties. At Dundry 

 A. carinata is rare, although it is usually found fairly 

 plentifully elsewhere, in fact, wherever the upper beds 

 of the Inferior Oolite are exposed in this neighbourhood. 



The Middle Lias of the Ilminster district has yielded 

 excellent examples of the type species. 



It should be borne in mind that Aulacothyris is only a 

 stage of development giving rise to forms without the 

 furrow, which are called Zeilleria. The young of lechenhyi, 

 anglica, etc., are often furrowed. Old forms of carinata are 

 not always furrowed, although they are more or less so in 

 the young state. 



CiNCTA, Quenstedt, 1871. (Type : C. cor, Lam. sp.) 



Etym. — cinctus, a girdle. 



Beak small, acuminated and pointed, very strongly cari- 

 nated ; foramen excessively small. Shell broad, sometimes 

 transverse, greatly depressed although convex in both 

 valves ; frontal region sharply truncated. This group is 

 only met with in the Lias (12, p. 275). 



The above diagnosis of Gincta is given by Deslongchamps. 

 (Ehlert does not give any diagnosis ; he simply quotes it as 

 a section of his sub-genus Eudesia under the genus Magellania. 

 Quenstedt divided the Brachiopoda into several groups. 



