METER — ON A NEW SPECIES OF TEEEBEATELLA. 
1G7 
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 vride ; 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 cro.^sed 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. JSIenardi, 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 
4^ lines in breadth by 4 in length ; another specimen measures 5^ 
lines in breadth by 4 in length ; the largest ventral valve measures 
5i in breadth by the same in length, and, as in this specimen the 
beak is nearly perfect, one may suppose the length and breadth in 
this species to be nearly equal ; the greatest breadth of the shell is 
usually close to the hinge line. 
Approaching most nearly in form to T. Menardi, this species is, 
however, readily distinguished bv 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 quarry 
about a quarter of a mile west of St. Katheriue's Hill, near Gruild- 
ford, where it occurs in company with T. Menardi, Lam., T. ohlonga. 
Sow., and TerehratuUna striata, Wahl., var. (T. auriculata ?, D'Orb.) ; 
these are, however, all extremely rare. 
8, Church Buildings, Clapham Common. 
Explanation of Plate XII. 
Fig. 1. Dorsal valve, magnified; 4. Front view of ditto; 5. Another dorsal valve; 
6. Inferior of ditto, with medial septum; 2. Ventral valve; 3. Ditto, side view. 
