MEYER — ON A NEW SPECIES OF TEREBRATELLA. 



167 



sider this species as a Terebratella : the peculiar form of the dorsal 

 valve has suggested its specific name. 



Terebratella trifida, n. sp. Shell (judging from a comparison 

 of several single valves) as wide as long, in old specimens perhaps 

 rather longer than wide ; convex in both valves : dorsal valve mode- 

 rately convex, and divided into three portions ; a large, elevated, 

 mesial fold, in the shape of an acute rib, occupying the entire central 

 division, on either side of which, on the lateral divisions, there exist 

 one or two ribs of small elevation, followed occasionally by a third of 

 still smaller size ; the whole being crossed by numerous concentric, 

 strongly marked lines of growth. The hinge line is but slightly 

 curved. 



The ventral valve is much deeper than the opposite one, has a deep 

 angular sinus, and on each side of the lateral portions of the valve, 

 two or three ribs ; the beak seems to have projected but little, in one 

 of my specimens appearing to have been truncated almost as abruptly 

 as in T. Menardi, and showing evidence of a small flattened space or 

 hinge area between its ridges and the hinge line : the foramen is rather 

 large. 



The interior of one of the dorsal valves exhibits a small, elevated, 

 longitudinal septum, commencing from beneath the hinge plate, and 

 extending to nearly half the length of the valve. Shell-structure 

 punctuate. 



Dimensions. — The largest dorsal valve in my possession measures 



Approaching most nearly in form to T. Menardi, this species is, 

 however, readily distinguished by its very large and simple mesial 

 fold. 



The two first examples of this shell I obtained from a small quarry 

 near Tewsley, south of Godalming ; the others are from a quarrv 

 about a quarter of a mile west of St. Katherine's Hill, near Guild- 

 ford, where it occurs in company with T. Menardi, Lam., T. oblonga, 

 Sow., and Terebratulina striata, Wahl., Var. (T. auriculata ?, D'Orb.) ; 

 these are, however, all extremely rare. 



8, Church Buildings, Clapham Common. 



Explanation of Plate XII. J 



Fig. 1. Dorsal valve, magnified; 4. Front view of ditto; 5. Another dorsal valve; 

 6. Interior of ditto, with medial septum; 2. Ventral valve ; 3. Ditto, side view. 



