178 F. Chapman and Irene Grespin : 



face is covered with striae, 20 to 25 in number, which 

 in the adult stage are wavy and irregular. 



Occurrence. — Lower Cretaceous. Queensland. 

 Rhynchonella solitaria, Moore, 1870, p. 245, pi. X., fig. 10. 



The shell is wider than longer, with four widely 

 spreading costae, and a single lateral costae on either 

 side of the sinus. Costae evanescent towards the umbo. 

 Occurence. — Lower Cretaceous. Queensland. 

 Also Jurassic, Geraldton (cf. solitaria, — fide F. C. in 

 Nat. Mus. coll.). 

 Rhynchonella variabilis, Schlotheim, Moore, 1870, p. 231-232 (list),, 

 pi. X., figs. 11, 12. 



Shell as high as broad, about 9 costae, which are 

 plicated towards the anterior commissure. 



Occurrence. — Jurassic. Geraldton District, W. Aus- 

 tralia. 

 With regard to these Mesozoic Australian rhynchonellids it is in- 

 teresting to note that one of the forms from the Lower Cretaceous, 

 viz., R. rustica, agrees with the general form of the Miocene and 

 later Tegulorhynchiae. The shell is wider than long, though the 

 transverse character" is not absolutely uniform, but predominant. The 

 numerous costae also form another factor for comparison, although 

 the riblets in the later Tertiary and living forms tend to become 

 less numerous and less acute. The beak in Rhynchonella rustica is 

 said to be acute and compressed when young. In his description of 

 R. rustica,, Moore compares the Australian Cretaceous form with 

 R. concinna of the Great Oolite and Bradford clay of England which, 

 he says, " it approaches more closely." From the excellent figures of 

 R. concinna given by Davidsono, it will be seen that the delthyrlum 

 is almost exactly comparable with that in TegulorhyncMa, for the 

 deltidial plates are disjunct and are almost equiangular, and in no way 

 could R. rustica on this evidence be compared with the Cretaceous 

 genus Cyclothyris. R. rustica may also be compared with the com- 

 pressed and almost truncated beak in Tegulorhynchia. Two other 

 forms, both from the Cretaceous of Central South Australia and 

 Queensland respectively, are Rhynchonella eyrei and R. croydonev^is. 

 Both of these have the ornament characterised by the prominent 

 growth-lines which cross the riblets. In R. eyrei these are developed 

 into distinct laminae, and in R. croydonensis they also occur, but are 

 less distinct, and more distantly placed. 



In "Rhynchonella" variaMlis we have a type of shell which is 

 coarsely plicate, but the entire form of the shell is closely comparable 

 -with the variants of Tegulorhynchia squamosa, as we have them 

 represented at Waurn Ponds and Keilor. The dorsal valve in these 

 forms, is strongly ventricose, and the ventral valve is subplanate. 

 In regard to the beak in R. variaMlis, this is not prominent, and the 

 apex varies from being slightly incurved to almost truncate. This 

 seems to suggest the possibility, when compared with the other 



9. Davidson, 1852, pi. xvii., figs. 6-12. 



