83 



* shape, as may be seen in fig. 10, while adult individuals are 

 almost globose. It occurs at Bradford Abbas, Half-way House, 

 Crewkerne Station, and in other places. 



No. 20. RHYNCHONELLA SUBTETRAEDRA, Dav. Plate IV., fig. 



7-8. 



RHYNCHONELLA SUBTETEAEDBA, Dav. Ool. JBrach. Pal. Soc., pi. 

 xvi., fig. 9-12. 



Shell generally wider than long, transversely oval or sub-, 

 pentagonal, sometimes slightly longer than wide ; valves nearly 

 equally convex ; a wide mesial fold of moderate elevation oc- 

 cupies about a third of the breadth of the dorsal valve, and a 

 sinus of variable width that of the ventral one ; beak incurved ; 

 foramen small, surrounded by deltidial plates ; surface orna- 

 mented by a variable number of angular plaits, from twenty to 

 thirty on each valve ; length sixteen, width eighteen lines. 



This species varies very much in shape, and is sometimes 

 irregular, from the fold being twisted more to one side than 

 another, as is seen in JRh. inconstans and other species. It is a 

 common shell in the Bradford Abbas district. 



No. 21. RHYNCHONELLA SUB-ANGULATA, Dav. Plate IV., fig. 

 11-12. 



Shell more or less sub-pentagonal, and generally a little wider 

 than long ; dorsal valve more convex than the ventral one, and 

 divided into three portions, of which the central one forms the 

 mesial fold ; ventral valve moderately convex, with a wide 

 mesial sinus ; beak much incurved ; foramen small, margined 

 by deltidial plates ; valves ornamented by a variable number of 

 angular plaits, of which from ten to twenty -five may be counted 

 on each valve ; of these, five or six occupy the fold or sinus ; 

 length about nine lines, by ten in breadth. 



This has not been a w r ell-understood species. I believe it to 

 be a variety of Sowerby's figure, if I am to judge from the 

 specimens I have seen from the Inferior Oolite of Cheltenham, 

 Bradford Abbas, and some other places, and which have been 

 referred, by myself and others, to Sowerby's species. 



