SUPPLEMENT. 3 



Dimensions. — Length of the specimen in Pig. 1 21 lines; height 16 lines; convexity 

 of a single valve 5 lines. Fig. 2, a more imperfect specimen, has the ornamentation 

 more strongly defined. A third example retains little more than the ornamented portion 

 of the surface ; a fourth specimen is smaller and nearly entire in outline, but retains 

 little more of the surface than the irregular lines of growth. 



% 



Trigonia infra-costata, Lycett. Sp. nov., figs. 3 and 4. (Fig. 4 enlarged one diameter.) 



Of this small species of the Costata, I have only a single imperfect example, 

 fortunately the portion preserved possesses all the features necessary to characterise the 

 species ; it is remarkable for the unusual prominence of the ornamentation upon the 

 escutcheon and the area, and more especially for the great breadth of the escutcheon ; 

 the costae (of which about seventeen are preserved) are narrow, very prominent, and 



Fig. 3. 



Fig. 4. 



Trigonia infra-costata, from Spain. 



much marked transversely by decussating lines of growth which indent their surfaces, 

 rendering them slightly nodulous ; their posteal extremities are well separated from the 

 marginal carina, which is large, and has its tubercles unusually prominent ; the inner 

 and median carinae are well-defined ; there are also some small inter-carinal costellse. 

 The escutcheon is very wide and flattened, its large irregular tubercles give to it 

 a roughened nodose aspect. The umbones are narrow, prominent, and recurved. 

 The anterior side is somewhat compressed and sinuated. Apparently, the shell if 

 perfect would have more than twice the height of the portion preserved. It was 

 associated with T. Oviedensis, and appears to be more rare than that species. 



By referring to the comparison of the genus Myophoria with the Costata at p. 215 of 

 this Monograph, the above description of the present species will show that both by 

 its figure and surface ornaments it is clearly separated from Myophoria, and that it 

 possesses all the attributes of the Trigonia costata, even more strongly developed than is 

 usual with that section. The curvature of the umbones is more especially well marked, 

 and would alone suffice to establish its generic identity. 



