256 Mr. J. Lycett on some new species 0/ Trigonia 



an Oxford clay species ; in that shell however the umbones are 

 more recurved, the carinas have much larger tubercles, and the 

 median carina has in addition a series of transverse varices which 

 are absent in T. decor ata. It has sometimes been mistaken for 

 T. clavellata, but differs from that well-known form in the fol- 

 lowing particulars. 



The Inferior Oolite shell is less elongated, the umbones are 

 not recurved, the posterior border is not concave, the general 

 figure has less convexity, the area is more flattened, and the lan- 

 ceolate space is much smaller and not striated; the rows of 

 costae are more numerous ; the tubercles are more numerous, 

 more closely arranged and less prominent. Another large cla- 

 vellated species, the T. muricata, Goldf., approaches more nearly 

 to the figure of our shell, but the Portuguese species ha3 the area 

 much more narrow, the costae are less numerous, but much more 

 elevated, the tubercles being larger and more distantly arranged. 



The figure likewise closely agrees with T. Bronnii, Ag., from 

 the Terraine h Chailles or Oxford clay ; but the ornamentation of 

 our species, both upon the area and the sides of the shell, is more 

 minute and delicate, with more numerous rows of costae, the 

 carinse having no distinct elevation as in the species of Agassiz. 



Trigonia decor at a occurs abundantly in the Trigonia grit 

 throughout the Cotteswolds, but the test is very fragile, and is 

 difficult to detach from the hard matrix. Rodborough Hill near 

 Stroud has produced it in great numbers. 



Trigonia gemmata, Lycett, n. sp. PI. IX. fig. 8. 



Shell small, ovately trigonal, excavated and somewhat rostrated 

 posteriorly, rounded anteriorly ; umbones obtuse, somewhat re- 

 curved, surface moderately convex; area narrow, transversely 

 striated and bounded on each side by a narrow, elevated and 

 striated carina, which is also gracefully curled ; costae numerous, 

 closely arranged, elevated, acute ; the upper third of the valves 

 has concentrically curved and finely tuberculated costae, those 

 which succeed are directed from the carina obliquely downwards ; 

 they are straight, are regularly and densely serrated, the spaces 

 between the costae forming narrow deep grooves. 



T. duplicata, Sow., approaches our shell in the general figure 

 and in the arrangement of the costae, but the latter costae of 

 T. duplicata are dichotomous and waved, the serrations being 

 irregular ; neither of these features are observable in our shell. 



It is very rare ; the largest specimen is an inch and a quarter 

 in length upon the marginal carina, and an inch in the opposite 

 direction. I have only seen two specimens. 



Near Nailsworth, in the freestone beds. 



