408 PROCEEDINGS OF THE ACADEMY OF 



Localities. Marshall and the grindstone quarries at Pt. aux Barques, be- 

 longing to the Marshall group. 



The dorsal valve greatly resembles that of R. circularis. 



Rhynchonella Makshallensis, n. sp. Shell of medium size ; dorsal valve 

 very ventricose, with the middle region somewhat flattened, and all the mar- 

 gins abruptly deflected the anterior at nearly right angles ; beak prominent, 

 obtuse, incurved ; cardinal slopes short, making with each other an angle of 

 about 100. Surface of valve marked by about 27 medium-sized rounded, 

 radiating plications, two or three of which are implanted on each lateral ex- 

 tremity, some of tbe plications reaching the beak. A shallow mesial fold 

 rises in about the middle of the valve and embraces seven plications. The 

 mesial septum extends about one-eighth the length of the valve. 



Length of the dorsal valve -58 (100) ; breadth -62 (107 ; convoxity, -30 (52). 



Locality. Marshall. 



Rhynchonella camekifeka, n. sp. Shell of moderate size, tumid ; beak of 

 ventral valve projecting and slightly upturned ; cardinal slopes straight, at 

 right angles ; sides of the shell rounded ; front margin similarily rounded or 

 somewhat straight, not unfrequently produced on one side of the mesial sinus. 

 Dorsal valve nearly circular, a little more convex than the ventral, most con- 

 vex anterior to the middle, and rather abruptly bent down in front. Ventral 

 valve with a shallow sinus, which extends back about one-fourth the length 

 of the valve, corresponding to the fold in the dorsal valve ; most convex be- 

 tween the beak and the middle ; dental plates parallel, well developed ; teeth 

 at right angles, elongate, growing stouter anteriorly, with handsomely crenu- 

 lated margins ; mesial partition of the dorsal valve, extending nearly one half 

 its length, thickening near the beak, to give space for the excavation of a 

 small chamber within the septum. Shell with 20 or 21 (a variety ? with 16) 

 sharp plications, of which three or four are comprised in the mesial sinus ; 

 these are crossed by a few squamulose concentric wrinkles ; shell structure 

 fibrous. 



Length of an average specimen -38 (100) ; breadth *34 (90) ; thickness, 

 19 (50). 



Locality. Pt. aux Barques, in a conglomeritic ferruginous sandstone over- 

 lying the gritstones of the Marshall group myriads of casts sometimes form- 

 ing, with Centronella Julia, the whole mass of the rock. 



The small chamber in the mesial septum of the dorsal valve is an interest- 

 ing and unique character. On a similar cameration of the septnm of the ven- 

 tral valve of some Cyrtise the genus Cyrtina has been founded ; and Professor 

 King established his Camarophoria on the formation of an arch in the ventral 

 valve by the approximation of the dental plates. 



This species has the external appearance of the young of R. wcuebescens, 

 but, amongst thousands, none attain proportions very different from those 

 given above. 



Rhynchonella bakquensis, n. sp. Shell small, transversely oval, thin. 

 Ventral valve with a moderately prominent beak and slightly curved cardinal 

 slopes ; greatest tumidity near the beak, from which the surface descends in 

 a nearly right plane to the anterior margin, and with little convexity to the 

 right and left margins. Dorsal valve flattish, most inflated in the middle. 

 Mesial fold and sinus small, traceable one fifth or sixth the length of the shell, 

 embracing two or three sharp plications, of which the entire surface of each 

 valve receives about 12 or 13. Dental plates of ventral valve parallel; me- 

 sial septum of dorsal valve camerated as in R. camerifera. 



Length -30 (100) ; breadth -32 (107) ; thickness -13 (43). 



Locality. Grindstone quarries, Pt. aux Barques, with R. camerifera. 



Rhynchonella subcibcularis, n. sp. Shell small, cuneate-rotund, subtumid. 



[Sept. 



