252 CARBONIFEROUS LIMESTONE BRACHIOPODA. 



about three lines from the beak, the two large mesial ridges 

 simple, having besides a small dichotomous pair on each side in 

 the sinus. Width 6 lines, proportional length of receiving valve 

 about y^Q^Q, length of entering valve -f-^p^, width of sinus in 

 front margin about -j-^q, depth thereof jy)j, depth of receiving 

 valve at middle of side j^-^, greatest depth of entering valve 

 Y^\ ; the three mid-ridges at margin occupy a space of 2 lines, 

 six of the lateral ones occupy the same space, surface smooth. 



The great number of small obtuse dichotomizing plaits on the 

 sides distinguishes this from any of the varieties of A. flexistria, 

 A. ventilabrum, &c., as well as their extending quite to the beak, 

 and the disproportionally large mesial ridges separate it from the 

 A. bifera and A. cuboides. I have not seen the dental lamellae. 



Rare in the carboniferous limestone of Derbyshire. 



(Col. University of Cambridge.) 



Hemithyris long a (M^Coy). 



Desc. Longitudinally trigonal, length exceeding the width or 

 depth, greatest width at one-third from the front margin, 

 lateral anterior margins obtusely rounded, front very obtusely 

 angulated in the middle ; posterior lateral margins long, nearly 

 straight, converging to the beak at an angle of 80°; commis- 

 sure with a slight w^ave towards the entering valve in the pos- 

 terior half of the lateral margins ; anterior half of the lateral 

 margins nearly straight, with a very faint indication of one 

 plate on each side ; middle of the front margin elevated at an 

 angle of 85° with the plane of the lateral margins into a wide 

 tongue-shaped sinus with sigmoid sides, acutely angular in 

 the middle ; entering valve with the profile very slightly 

 arched, greatest depth about the middle of the length ; sides 

 convex, arched abruptly downwards on each side from the 

 obtuse mesial line ; receiving valve flattened or very slightly 

 convex for about three lines from the beak, after which the 

 very narrow sides alone are continued nearly straight to the 

 obtusely rounded anterior lateral angles, the wide mesial por- 

 tion being strongly depressed to fill the sinus in the front 

 margin ; beak rather large, very slightly incurved ; surface 

 smooth, with a few obtuse imbrications of growth near the 

 margin ; tissue very coarsely fibrous, almost visible to the 

 naked eye ; dental lamellse in beak of receiving valve very 

 short, subparallel, slightly divaricating ; mesial septum of en- 

 tering valve very minute. Length nearly 6 lines, proportional 

 width f-^-^y length of entering valve f-^^, depth of entering 

 valve y*^^^, depth of receiving valve y^^^, width of sinus j-^^, 

 depth thereof -^^-q. 



