﻿CRETACEOUS BRACHIOPODA. 



35 



crassa, and rustica can be fairly matched among the specimens of T. sella from 

 Shanklin. A comparison of the same Shanklin species with my specimens from 

 Faringdon has also led me to conclude that many of the forms attributed to T. Roemeri, 

 and all of the supposed T. biplicata of the Sponge-gravels, are referable to the Shanklin 

 variety of T. sella. It is true that in the generality of the Faringdon specimens the 

 foramen is larger than in any of those met with at Shanklin, but then it appears to me 

 that the large size of the foramen is a feature peculiar to all the Faringdon Brachiopoda, not 

 excepting Waldheimia tamarindus. With regard to Terebratula biplicata, all the specimens 

 which I have seen from the Upper Greensand have the beak so closely incurved as almost 

 completely to hide the deltidium, as represented in your Monograph, PI. VI, figs. 1 to 42. 

 I should, therefore, question the identification of the figures 45 to 49, PI. VI, as well as 

 figures 36 — 37, PI. IX of your Monograph, all of which might probably be referable to 

 the Shanklin variety of T. sella' 7 



Mr. Meyer is so accurate an observer that I feel anxious his observations in con- 

 nection with this difficult question should be duly considered. 



It will, I think, be preferable for the present, at least, to group the different forms 

 of T. sella into three or four varieties, namely — 



35. Terebratula sella, Sow. Dav., Cret. Mon., PI. VII, figs. 4 — 10. 



There can be no doubt that the figures above quoted represent the typical forms of 

 Sowerby's species, as occurring in the Lower Greensand of the Isle of Wight. The loop 

 is short, simple, and wide as compared with that of T. biplicata. T. sella ranges from the 

 " Perna-bed " to the top or nearly the top of the Lower Greensand, but does not appear to 

 enter the Gault or pass above it. 



36. Terebratula sella, var. Upwarensis, Walker. Sup., PI. V, figs. 3 to 10 a. 



Terebratula sella, var. Upwarensis, Walker. Geol. Mag., vol. vii, 1870, p. 562. 



Mr. Walker describes this variety as " globular, deeply plicated, sides of the 

 shell compressed, surface smooth, marked by faint concentric lines of growth ; ventral 

 valve very much incurved, the deep plications extending about two thirds of the length 

 of the valve, forming a central elevation on each side of it, and a deep depression, 

 again rising into an elevation ; thence, bending at right angles, it forms the flat side 

 of the shell ; the upper third of the shell is somewhat convex ; the beak curved, short, 

 truncated by a large round foramen, the margin of which is thickened at the sides ; 

 the beak-ridges rounded ; deltidium in one piece, shallow and wide ; dorsal valve 



