Mollusca from the Bokkeveld Beds. 251 



Actinopteria aff. hoijdi (Conrad). 



sp. 

 Modiomorpha haini (Sharpe). 



„ cf. inmentana, Hartt and Eathbun. 



aff. seUoivi, Clarke. 



OETHONOTA aff. UNDULATA, Conrad. 

 (PI. XXXI., fig. 2.) 



There is one specimen (No. 101) of a species of Ortlionota showing 

 both valves in apposition, which is ahnost identical with 0. undulata, 

 Conrad," of the Hamilton Group of the United States. The shell 

 is extremely elongate, widening a little posteriorly, with nearly 

 parallel dorsal and ventral margins (the front portion of the basal 

 margin is broken in our specimen) ; the length is three times the 

 greatest height. The basal margin is nearly straight ; the cardinal 

 line is quite straight ; the anterior end is very short and rounded ; 

 the posterior end is obliquely truncated. The valves are moderately 

 convex ; the beaks are subanterior, being about one-eighth the 

 length of the shell from the front end, and are small, low, directed 

 forwards and rising a little above the hinge-line. The umbonal 

 ridge is straight, prominent, and angular, extending to the posterior 

 Imsal margin. The post-cardinal slope is wide and marked by one 

 In-oad angular fold along its middle and a smaller fold along the 

 hinge-line with a wide angular groove between them. The surface 

 of the shell is marked by fine concentric strige, and a few strong 

 ■concentric undulations are present near the anterior end and upon 

 the cardinal slope. 



Dimensions. — Length 58 mm. ; height 19 mm. 



Affinities. — As above remarked, this shell closely resembles 

 Ortlionota undulata, Conr., in most characters ; the proportions are 

 identical ; but the oblique truncation of the posterior end and 

 angularity of the umbonal and post-cardinal ridges are distinctive 

 features, and recall those of the much more elongate 0. carinata, 

 Conr.,t also of the Hamilton Group. 



Locality. — (No. 101) Shales al)ove 3rd Sandstone, Tunnel Siding, 

 Hex Kiver Pass. 



* Hull, Palseont. New York, vol. v., pt. i., Lamell. ii., 188-5, p. 478, 

 figs. :37-42. 



t IhhL, p. 47U, pi. Ixxviii., figs. 34, 35. 



