The Invertebrate Fauna of the Uitenhage Series. 199 



Formation." In the description of the Madagascar fossils, the 

 opinion that these two forms are truly related was not expressed, 

 and it is not necessary to infer that such a view was actually 

 entertained. 



Kilian * has suggested that H. baini may represent an immature 

 stage of H. atherstoni (Sharpe), but this is certainly not the case. 

 H. atherstoni at a comparable growth-stage is much more finely 

 ribbed, to mention only one point of distinction. 



With regard to the type-specimen of Ammonites baini Sharpe, 

 preserved in the collection of the Geological Society, it is perhaps 

 well to note that in the late Prof. J. F. Blake's published list of the 

 types and figured specimens in the Society's museum, reference is 

 accidentally made to a wrong specimen.! The individual figured by 

 Sharpe was unfortunately overlooked by Mr. C. D. Sherborn when 

 preparing a manuscript catalogue of the collection some years ago. 

 The specimen erroneously noted as the type (registered 10976) was 

 presented by Atherstone and bears the date 1876 ; J I consider it to 

 represent a hitherto undescribed form, and it is dealt with in these 

 pages under the name Holcostephanus modderensis. 



HOLCOSTEPHANUS cf. BAINI (Sharpe). 

 Plate IX., fig. 2 ; X., fig. 1. 



A single specimen, from the collection in the South African 

 Museum, agrees so closely with Sharpe' s Ammonites baini that 

 it has seemed questionable whether it should not be considered 

 identical. 



Description. The specimen, which is considerably larger than 

 known examples of H. baini, consists of at least four whorls, and 

 the form of these as well as the degree of overlap in the earlier 

 whorls is the same as in H. baini. Some of the shell substance is 

 retained and the specimen is partly preserved as a cast, but it 

 exhibits in very imperfect manner the course of the septal sutures, 

 so that these cannot be satisfactorily copied for illustration. The 

 body-chamber is not preserved. In the interior whorls the umbilical 

 wall of each whorl falls upon the umbilical tubercles of the pre- 

 ceding whorl, but in the latter half of the last whorl the degree of 

 involution becomes slightly reduced, so that the nodes of the 

 preceding whorl are completely exposed and the beginnings of the 

 Hank ribs proceeding from them can be just discerned. At the same 



* Kilian (4), p. 865. t Blake (2), p. 59. 



J Sharpe's figure of H. baini was published in 1856. 



