14 THE im.\cniotot)A. 



011I3' very slightly blpllcatocl, as reprosented in figure 1 1. Thoy 

 occur witli it, and arc commoucr. 



6. — Terebhatula DORSorLAXA, Waafjen. 



1867. Terei3. DonsorLAXA, Waagcn, Gcogn. Paliiont. Bcitriige 

 plato xxxi. (8), figure 7. 



A ratlier strongl}^ biplicatod species, -svliicli might, at first 

 sight, be taken for the j^oung of Tcrcb. perovalis, but wliich is 

 really easily separable. It has a medium sized rounded fora- 

 men, and its beak ridges are slightly produced near the beak, 

 and then thrown back as it were, thus giving to the shell on 

 each side of the beak a peculiarly folded appearance. Another 

 distinction is the well marked carina down the middle of the 

 larger valve, beginning at the beak. Its valves are always more 

 or less thickened at their junction, both at the sides and base of 

 the shell. Those characters are slightly modified in some of the 

 Iroad specimens. Waagen says that it differs from Tereh. infra- 

 oolithica, E. Desk, on account of the keel down the middle 

 of the larger valve. Our specimens are certainly far larger 

 than those figured by Dr. Waagen, and are from the zone of 

 Murchisonae. He quotes it from the Sowerbj'i zone ; but I 

 have not yet found this species there. Our specimens would 

 seem to stand in shape, etc., between Tereb. infra-oolithica and 

 Tereh. fcroimlis. The characters that I have mentioned above 

 will well distingu'sh it from Tercl. perovalis, specimens of which 

 are found in the same bed with it. Terel. dorsoplana is rather 

 uncommon, and I only know of two places where it has occurred 

 in this district. 



Localities. — Marston-road and near Sherborne (Dorset). 

 Waagen c[uotes it from Gingen (Wiirtemberg), Gunsberg (Canton 

 Solothurn), and La Eoche Pourrie, near Salins (Jura). 



Bimensions. — Length 1 inch 4 lines, breadth 1 inch 3 lines, 

 depth 10 lines. Another Specimen. — Length 1 inch 6 lines, 

 breadth 1 inch 3 lines, depth 10 Hues. Of a Broad Specimen. — 

 Length 1 inch 7 lines, breadth 1 inch 7 lines, depth 1 1 lines. 



