from the Inferior Oolite of the Cotteswolds. 255 



sequently the marginal carina is more curved and elongated ; the 

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

 and more distantly arranged ; they form with the costae 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 costae are more 

 closely arranged in T. v.-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 costae, 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 costae is nearly similar, but in our 

 species they are much more numerous. 



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

 the middle or freestone division near to Stroud, and my friend 

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

 upper division near to Cheltenham. 



Trigonia decor ata, Lycett, n. sp. PL IX. 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 carinae, 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 

 divisional sulcus, which passes parallel to the median row of 

 tubercles upon the area. The clavellated portion of the shell 

 has a very numerous series of rows of concentric tubercles; the 

 tubercles are small near to the marginal carina, and become 

 larger towards the middle of the curvature ; they are distinct, 

 rounded, closely arranged (15 or 16 being contained in a row), 

 the number of rows being about twenty, the whole of which are 

 distinctly tuberculated ; the lines of growth upon the sides of the 

 shell are fine and distinct. The dimensions are equal to the 

 largest examples of the clavellated Trigonia. 



This elegant shell is nearly allied to T. perlata, Ag., which is 



