from the Inferior Oolite of the Cottesivolds. 233 



anterior border obliquely downwards and backwards nearly 

 straight to the middle of the shell, and there form acute angles 

 with varices which proceed upwards nearly vertically to the mar- 

 ginal carina; the varices are slightly nodulous, they are fewer 

 and larger than the anterior costse. The first eight or nine 

 costse form only curvatures, and are not broken into two por- 

 tions. 



The species which approaches most nearly to the present shell 

 is T. angulata, Sow., but the figure of the two is different ; the 

 latter shell is more elongated and rostrated, the posterior border 

 is much more concave, the umbones are more recurved, and con- 

 sequently the marginal carina is more curved and elongated ; the 

 costse are less numerous, less regular, and the varices are larger 

 and more distantly arranged ; they form with the costse rather an 

 undulation than an angle, and are more conspicuously tuber- 

 culated. 



In the young state the two forms would more nearly re- 

 semble each other, but even in that condition the costse are more 

 closely arranged in T. y.-costata. Some examples in the British 

 Museum of a Trigonia collected by Miss Baker in the ferruginous 

 Oolite of Northampton may be the young condition of the spe- 

 cies ; to the same species may also be referred some small shells 

 from the Dogger of the Yorkshire coast; these have smooth, 

 straight, oblique costse, bent at a considerable angle, and have 

 been labelled in collections T. angulata. The small T. tripartita, 

 Forbes, from the Oolite of the Hebrides, has a certain degree of 

 resemblance to our species, but the varices in that shell are fewer 

 and much larger. 



From T. undulata, From., our shell is distinguished by the less 

 convex form and absence of large tubercles upon the marginal 

 carina ; the arrangement of the costse is nearly similar, but in our 

 species they are much more numerous. 



In the Cotteswolds T. y.-costata has occurred very rarely in 

 the middle or freestone division near to Stroud, and my fi-iend 

 Dr. Wright has obtained two specimens in the ragstones of the 

 upper division near to Cheltenham. 



Trigonia decorata, Lycett, n. sp. PI. XI. fig. 1. 



Shell ovately trigonal, somewhat depressed ; umbones obtuse 

 not recurved, anterior and inferior borders rounded, posterior 

 border lengthened and straight ; area flattened, striated trans- 

 versely, ornamented with three faintly traced carinse, or rather 

 as many lines of closely arranged very small regular tubercles, 

 the inner carina having in addition at its upper part a few irre- 

 gular transverse plications or varices ; there is also a median 



