Dr. A. Vaugliaii on Scnilnula. 195 



'I'lie figure of the species given in the * Geoh)gy of Y'uk- 

 sliirc/ |)t. 2, |»1. xii. fi.:^. 3, is a good and truthful representa- 

 tion of a specimen in the Gilbertson Collection (Brit. Mus.) 

 which has been type-labelled without any expression of 

 (loul)t. The figure is very slightly enlarged, as is usual with 

 all I'hillips's diawings, but tiiere cannot be any reasonable 

 doubt that this sj)ecinien is the holotype of the species, and 

 no such doubt has been previously suggested. 



Description of the IIoloty|)e of Terebratula penta'edra, Phill. 

 (the Genotype of Seminulu). 



Tiic tyj)e specimen lias lost the greater part of its test, 

 and consequently the characters of the external ornament are 

 not so obvious as could be desired. 



Form. — The size and outline of t!ie shell agree closely with 

 those of the holotype of SpirifHr ainbiyimn, Sjw., with which 

 1 have carefully compared Phillips's specimen ; the two shells 

 have the same pentagonal outline, the same position of 

 maximum width, and tiie beak is " produced " in the same 

 manner in each. Whereas, however, Spir. ambiguus is 

 strongly convex, Ter. pentaedrd is rather strikingly tiattencd 

 (a character reminiscent of Ter. hastatii, Sosv.). 



JJini/e-/ine and Fold. — Tiie valve-intersection is continu- 

 ously curved in the beak-region ; it lies completely in one 

 plane, except for the shallow lobe which marks the extremity 

 of the mesial fold. 



'J he mesial fold is marked out on the cast by two strong 

 radial ridges, separated by a broad shallow de])ressioii, and 

 the whole fold is raised but little above the level of the 

 flanks. 



In Spir. amhiguus, Sow., the mesial fold is formed on the 

 same pattern, imt is prominently raised above the flanks of 

 the shell. 



Pediclt-valve. — The test being partly removed from the 

 beak-region, the cast of the pedicle-cavity is satisfactorily 

 exposed ; it exhibits a narrow flattened area, bounded on 

 either side by a precipitous drop, indicating the presence of 

 strong dental plates. These characters are possessed iu 

 common by all Athyrids. 



There is no evidence as to the size of the aperture. 



Structure of 'Test. — The test, where preserved, is minutely 

 fibrous and impunctate, but it is doubtful whether the outer- 

 most layer ot the test is anywhere present. 



Surface-ornament. — (a) Concentric. Two or three con- 

 centric ridges on the cast indicate marked growth-halts. 



