146 Annals of the South African Museum. 



Th. caucasica (Eichwald),* from "Greensand" in Daghestan, said 

 to be of Gault horizon. When compared with other representatives 

 of the genus, this, like the African form, is of relatively elongated 

 outline ; but in Th. caucasica the shell is slightly more equilateral 

 and the posterior border is not so abruptly truncated as in Th. 

 papyracea, but is more convex in profile, while the course followed 

 by the anterior limb of the angular line on the cast is a different 

 one. 



Although the true systematic position of the genus Thetironia 

 cannot yet be said to be established beyond doubt, it is clear that 

 the angular linear marking on the internal casts in no degree coincides 

 with the course of the pallial line. The genus has therefore been 

 erroneously held to be related to members of the Veneridae, but 

 although its suggested affinity to the Lucinidae seems to accord 

 better with what is known of its characters,! yet the evidence for 

 such relationship is not of a satisfactory character. Mr. H. Woods, 

 who has examined some material which is very favourably preserved 

 for the purpose of comparative study, has found points of analogy 

 between Thetironia and Protocardia, both in the characters of the 

 hinge and the ornamentation ; but after drawing attention to some 

 features which distinguish these genera, and carefully weighing the 

 available evidence, Mr. Woods concludes that " although Thetironia 

 resembles the Cardiidae in several respects, yet the (points of difference 

 are too great to allow of its being included in that family." J 



THETIRONIA OBLONGA sp. nov. 

 Plate VII., figs. 12, 12a, 126. 



Description. The shell is of elongated form, with the length con- 

 siderably greater than the height. The umbones are situated a short 

 distance anteriorly to the middle of the shell and are fairly well 

 raised and prominent and are strongly incurved. The cardinal 

 margin is very long and is only slightly curved, falling very gently 

 when traced forwards from the umbo and still more gradually 

 posteriorly to the umbones. The greatest height of the shell is at 

 the umbonal part. The height near the posterior end of the shell is 

 greater than in the anterior quarter. In lateral aspect, the cardinal 

 margin is seen to pass by a curve into the posterior margin, which 



* Eichwald (1), p. 709, pi. xxvi., fig. 7; Anthula (1), p. 90, Taf. iv., fig. 6. 



t See remarks on this point by Miss E. G. Skeat ; Skeat and Madsen (1), p. 177. 



t Woods (3), vol. ii., part 4, p. 167 (1907). 



