402 



Walker — Greensand Brachiopoda. 



ventral valve being flattened towards the front margin. I originally 

 placed some of the specimens on which I found this species among 

 the varieties of T. pralonga, and others among those of T. extensa. 

 Mr. A. Wanklyn having kindly made for me some microscopic 

 preparations of the shells of Terehratulidce from the deposit at 

 Ui3ware, we found that these doubtful specimens presented a pecu- 

 liar and accordant structure, quite distinct from that of both T. extensa 



Fig. 3. 



Fig. 4. 



Fig. 1. Terehratula prwlonga, Sowby, magniiied 75 times. 



,, 2. ,, extensa, Meyer, ,, ,, 



„ 3. ,, microtrema, sp. nov. ,, „ 



„ 4. ,, Lankesteri, „ „ „ 



and T. prcelonga. In all the specimens of all forms of this species 

 which we have examined, the shell has very small and widely 

 separated perforations, as shown and contrasted with the structure of 

 T. extensa and T. prcelonga in Woodcut, Fig. 3. 



Terehratula Lanlcesteri, sp. n. PI. XIX. Fig. 2. — Shell ovate, 

 elongate, tapering towards the beak, rounded towards the front 

 margin. Dorsal valve moderately convex, widest near its middle. 

 Ventral valve very much arched, widest near the middle, bent almost 

 at a right angle near the front margin, and tapering considerably 

 towards the beak ; beak very much incurved, truncated by a large 

 foramen ; deltidium moderately wide but very shallow, in one piece ; 

 beak-ridges ill defined ; front margin of the valves flexuous. Shell- 

 surface marked by fine longitudinal striae on both valves, and with con- 

 centric lines of growth; loop probably short. Shell structure, — the per- 

 forations are smaller and wider a^oart than in T. prcelonga. This species 

 may be distinguished from T. prcelotiga, by its surface being covered 

 with fine stride, by its more oval shape, the absence of plications at 

 the front margin, the tendency of the front margin to become inflated, 

 by its shell structure, by its beak being more incurved, and by the 

 deltidium being shallower. From T. Dallasii it differs by being longer 

 and more oval, and by its striated surface. From T. capillata, by being 

 more elongated, by its ventral valve being more tapering towards 

 the beak, by the dorsal valve being less convex, and by its beak 

 being longer. The specimen here figured was obtained by Mr. N. 

 Moore, of St. Catherine's College, Cambridge, who kindly gave it to 

 me. Dimensions: length, 1.625 inches; breadth, 1 inch; thick- 

 ness, 1.04 inches. 



A small specimen figured, PI. XIX. Fig. 3, is probably a young 

 examjDle of T. Lanlcesteri. It exhibits the same general outline of the 

 ventral valve, and the surface is covered in the same way with fine 

 longitudinal strise. Dimensions : length, 1*1 inches ; breadth, '75 

 inches ; greatest thickness, -375 inches. I have much pleasure in 

 naming this species after E. Kay Lankester, Esq., B.A. 



