SCAPHOIDE^E. 15 



area, with its tuberculated bounding carinas and transverse striations, to perceive that it 

 cannot be allowed to remain in that section. 



Stratigrapldcal position and localities. This is a delicately ornamented species 

 occurring not uncommonly in the Upper Trigonia-grit of the Inferior Oolite in the 

 Cotteswolds at numerous localities ; impressions in the hard ragstones are common, but it 

 is difficult to separate a specimen in good preservation from the hard matrix. It also 

 occurs in the Inferior Oolite of the Half-way House Quarry near to Yeovil. In France, 

 Gueret is the locality for T. Proserpina, D'Orbigny. 



Trigonia gemmata, Lye. Plate I, fig. 7. 



Trigonia gemmata, Lycett. Ann. and Mag. Nat. Hist, 1853, pi. ix, fig. 8, p. 425. 

 — — Morris. Catal., 1854, p. 228. 



Shell ovately trigonal, moderately convex ; umbones elevated, pointed, and slightly 

 recurved ; anterior border moderately produced, both it and the inferior border elliptically 

 curved ; hinge-border straight, lengthened, sloping obliquely. Area narrow, flattened, 

 transversely delicately striated, but near to the apex costellated, having two distinct, 

 delicately knotted, or cord-like carinas which circumscribe it. The escutcheon is narrow, 

 lengthened, and depressed, rendering that portion of the slope slightly concave. The 

 costated surface has a dense and salient ornamentation ; the first-formed series of costse, 

 about seven in number, occupy more than half of the valve. They have the rows very 

 closely arranged, narrow, ridge-like, and concentric, each bearing a row of small, closely 

 arranged tubercles ; the succeeding rows of costse, eight or nine in number, are similar, 

 but they descend almost perpendicularly, or inclined somewhat forwards from the 

 marginal carina to the pallial border. There is also a third series of short or supple- 

 mentary costse, which, originating at the anterior border, pass obliquely upwards to be 

 united to the side of the last-formed costa of the first series, or concentric costse, producing 

 a singular unsymmetrical but not inelegant aspect to the anteal side of the valve. There 

 are eight of these short costse. The perpendicular costse are undivided ; one specimen 

 only has a single intercalated rib ; the tubercles upon the rows are irregular and unequal. 



Length, 18 lines upon the carina; the diameter at right angles to it is 15 lines. 



Trigonia duplicata, Sow., is allied to our species, and differs from it in the following 

 particulars : — The species of Sowerby is less convex, and has the ornamentation smaller 

 and more irregular ; it commences with only two or three concentric or horizontal costse, 

 all the others are directed perpendicularly downwards from the carina ; they are irregularly 

 knotted, are frequently and sometimes alternately dichotomous ; they are also fewer and 

 more widely separated ; the anterior side of the valve has also a few curved and very 

 irregular and narrow costse. The differences here indicated are very persistent. 



