﻿SUPPLEMENT. 15 



a lengthened and concave hinge-border ; the siphonal border is comparatively short, 

 placed almost at right angles with the hinge-border ; the pallial border is lengthened 

 and curved elliptical]}'. Tiie sides of the valves have very numerous small tuberculated 

 costa3, at the umbonal extremity the first-formed three or four rows are subconcentric 

 and plain, the succeeding rows become angulated with small irregular tubercles ; the 

 rows continue small near to the pallial border and are somewhat irregular in their 

 direction ; about the middle of the valve they are united to a much less numerous 

 series of posteal costa3, which arc also tuberculated. The posterior costse are at first curved, 

 but the succeeding ones become more perpendicular and are directed downwards from 

 the marginal carina even to its posteal extremity. In adult forms the pallial costae near 

 to the border take nearly the direction of the lines of growth, and are small and crowded 

 with minute fringing papillae. 



The general aspect of the ornamentation presents an approach to Trigonia produda, and 

 is intermediate between that of T.produda and T. angulala ; the curve of the uncompressed 

 valve is, however, sufficiently distinct from either of those examples of the Utidulatte group 

 and renders its separation as a species necessary. The distinctness of the species may, 

 in fact, be recognised even in very young examples whenever they are well preserved, as 

 well as in the apical portions of the more adult forms. I have therefore figured three of 

 the smaller specimens collected by Mr. Walford and Mr. Windoes in Oxfordshire : the 

 collection of Mr. Vv'indoes contains two others of similar aspect, and also a much larger 

 specimen apparently almost of adult growth. The surface ornaments are for the most 

 part well preserved, but the posteal portion is too much truncated and imperfect to be 

 submitted to the artist. 



The largest of the Oxfordshire shells on our plate, figs. 3, 3 a, was obtained by 

 Mr. Walford at Hook Norton in the lower beds of the formation. The siu-face orna- 

 ments are well preserved, but the specimen unfortunately is very imperfect posteally and 

 is much flattened from vertical pressure. The acquisition of these specimens, together 

 with the fine adult forms collected by Mr. Witchell in the Cotteswolds, has enabled me 

 to discover and correct one of my own errors. The specimen attributed to T. angulata 

 (Trigon. Monogr., Plate XIV, fig. 5) collected about twenty-five years ago in the Upper 

 Trigonia-grit of Rodborough Hill, in its posteal portion is so defective and incomplete that I 

 always entertained doubts of the correctness of that identification: the more recently obtained 

 specimens in the Cottleswolds and in Oxfordshire enable me to separate this hitherto 

 doubtful form from T. angulata, and to unite it to the present species, which is now well 

 and sufficiently illustrated. The splendid and almost unique specimen from Mr. Witchell's 

 collection (Trigon. Suppl., Plate III, figs. 1, 1 a) was obtained by him near the hamlet of 

 Hyde in the parish of Minchinhampton in a whitish-grey limestone (Upper Trigonia-grit) 

 and cleared by him after the employment of much skill and labour. The specimen obtained 

 by Mr. Witchell (Plate III, fig. 2) from the Clypeus-grit of Rodborough Hill would 

 also be considered a very fine specimen in the absence of the Hyde specimen, and proves. 



