404 Walker — Greensand Brachiopoda* 



thickness, 1-1 inches ; but in the Woodwardian Museum, Cambridge, 

 there is a larger specimen, which was obtained by Mr. Henry 

 Keeping, who kindly gave me its dimensions. Length, 3*3 inches ; 

 breadth, 2-8 inches ; greatest thickness, I'O inches. I have 

 separated the convex specimens of this species, which have a short 

 and rounded beak as a variety or sub-species, under the name of T. 

 depressa var. cyrta, PL XVIII. Fig. 1 . Shell convex, inflated, width 

 and length nearly equal, becoming flatter towards the frontal 

 margin ; beak short, rounded, truncated by a large foramen. Beak 

 ridges ill-defined ; deltidium in one piece, wide, but shallow. Yentral 

 valve globose ; dorsal valve very globose towards the beak. Frontal 

 margin not plicated, the valves slightly flexuous. Shell surface 

 smooth, slightly marked by concentric lines of growth. Loop short. 

 Dimensions: length, 1-75 inches; breadth, 1-625 inches; thickness, 

 1*04 inches. 



This variety occurs at Upware and at Potton along with the typical 

 form, from which it differs by its greater convexity, by its beak 

 being shorter and more rounded, and by its deltidium being much 

 shallower. 



T. Dallasii, nobis, (Geol. Mag. Vol. IV. p. 455, PI. XIX. Fig. 1.).— 

 Since I described this species, I have obtained specimens of larger 

 dimensions. Length, 1-33 inches ; breadth, 1-12 inches; thickness, 

 •92 inches. A single ventral valve measures: length, 1*5 inches; 

 breadth, 1-25 inches. 



This species differs from globose specimens of W. tamarindiis, 

 with which it has been compared, in having its deltidium in one 

 piece, its beak ridges ill-defined and rounded, and the space between 

 them and the hinge line not concave ; the foramen is also larger. A 

 specimen presented by me to the York Museum has been cut open 

 by Mr. Dallas, who found that it has a short loop, somewhat resem- 

 bling that of T. depressa, to which this species is certainly most 

 nearly related. 



T. extensa, Meyer. PL XVIII. Fig. 5. — This species, — described 

 by Mr. Meyer as occurring at Godalming, in the Geol. Mag. Vol. I., — 

 occurs also at Upware, where it attains a large size, agreeing 

 with the Godalming specimens in form and in shell -structure. Some 

 varieties of this species approach somewhat in form to W. celttca, 

 but have a short loop. Dimensions : length, I'lG inches ; width, 

 •66 inch ; thickness, '5(d inch. 



Waldheimia Woodwardt, nobis. (Geol. Mag. Vol. IV, PL XIX. 

 Fig. 3.) — I have obtained several more specimens of this species; the 

 largest measures: length, 1^58 inches; breadth, -875 inch; thick- 

 ness, -75 inch ; the smallest specimen : length, -75 inch ; breadth, 

 •45 inch ; thickness, -375 inch. The dorsal valve of this 

 specimen is deeply channelled. The peculiar shape of the ventral 

 valve appears to be constant ; the deltidium is in two pieces ; the 

 dorsal valve is generally much more grooved than in the specimen I 

 figured. Since I described this species I have seen its loop, which 

 extends nearly to the front margin. This species is easily distin- 

 guished from specimens of W. celtica by the shape of its dorsal 

 valve, etc. 



