On the Teeth of the Pneumonobranchiate Mollusca. 329 



posit in anotherj the conditions having become unfavourable to 

 the perpetuity of their development in the latter deposit over the 

 original region whence they had migrated," 



There is now only one other part of our summary of fossils 

 which seems to claim attention, and that is the Echinodermata. 

 Of these at least six out of eight are common to the Inferior 

 Oolite, namely — 



Nueleolites = Clypeus. Holectypus = Galerites. 



1. sinuatus. 4. depressus. 



2. clunicularis. 5. Acrosolenia hemicidaroides. 



3. orbicularis. 6. Diadema depressum. 



Of these the Nueleolites sinuatus and Holectypus depressus are 

 highly characteristic of the Inferior Oolite. 



In concluding these remarks, it should be understood that 

 they refer only to a limited district. Were our observations ex- 

 tended over the whole range of the Cornbrash, as it occurs in 

 this country, we should doubtless arrive at additional facts, both 

 as regards the structure and agricultural capabilities and also its 

 fossil contents : we may indeed expect the list of the latter to be 

 greatly augmented, and in all probability other species common 

 to the Inferior Oolite will have to be noted in addition to those 

 in our present list. 



XXXII. — On the Teeth of the Pneumonobranchiate Mollusca. 

 By J. E. Gray, Ph.D., F.R.S., V.P.Z.S. &c. 



The teeth of the Pneumonobranchiate Mollusca are exceedingly 

 uniform, when this group is confined to those which have a 

 closed pulmonary cavity, which, in my former arrangement, I 

 called Adelopneumona ; I now think that the genera which form 

 the other suborder, being unisexual, and having many characters, 

 as well as the structure of the tongue, like those of the Tceni- 

 glossa, should be arranged with them, near to the Littorinidee, 

 which often pass the greater part of their lives out of water, 

 and have very imperfectly developed gills on the inside of the 

 mantle. 



All the genera of the order so restricted have very numerous, 

 nearly similar ctenoglossal teeth, placed in many cross lines on 

 a more or less elongated lingual band. 



In some genera the line is straight, in others angularly di- 

 verging from the central lines, and in some the series are angu- 

 larly bent on each side of the central line. 



Professor Troschel, who has figured the teeth of some European 

 Ann. ^ Mag. N. Hist. Ser. 2. To/.xii. 23 



