﻿Vol. 66.~] NON-1TAKINE MOLLT7SCA, ETC. FROM NYASALAND. 245 



Although the specimens are very numerous, they appear to be 

 referable to one particular species, and the presence of radial 

 striations (see PL XIX, fig. 16) is sufficient evidence for regarding 

 it as an example of Estheriella, a genus founded by Weiss to include 

 GiebeFs Posidonomya ivengensis and allied species from the Bunter 

 Sandstone of Saxony, which possessed the usual characters of 

 Estheria, but in addition a radially striated sculpture. 



Prof. Rupert Jones l has fully recognized the adoption of Esthe- 

 riella, and, in a final paper 2 on the subject, alludes to the presence 

 of radial striations on his species, Esiheria tegulata and E. tessellata 

 from the Upper Carboniferous of Scotland, the same character being 

 strongly expressed in Estheriella radiata (Salinas) var. midtilineata, 

 Jones, from the Trias of the Malay Peninsula, and more feebly so 

 in Estheria greyi 3 from the Karroo of Cradock (South Africa). 



The present species may be distinguished by the very anterior 

 position of the umbones, the nearly parallel condition of the dorsal 

 and ventral margins, and the truncated character of the anterior 

 end. In such details it appears to be a form which need not be 

 mistaken for any of those just mentioned, although in the clearly- 

 cut arrangement of the concentric sculpture and in some of the 

 valves showing a subquadrate contour, it somewhat resembles 

 Esiheria greyi. The integument of which these carapace-valves 

 are composed is most delicate and thin, a feature which would 

 account for their generally much wrinkled condition underpressure, 

 resulting frequently in the obliteration of the extremely fine con- 

 centric striations which otherwise form part of the sculpture. The 

 specimens also exhibit a glossy and iridescent aspect, indicating 

 certain mineral characteristics which prevailed during the period of 

 fossilization. 



Formation. — Permo-Carboniferous [Karroo Beds]. 



Locality. — Nkana (Andrews & Bailey). 



Conclusions. 



(a) The freshwater limestone of Chisali, containing remains of 



Yiviparus unicolor, is evidence in favour of an extension in 

 a north-westerly direction of the waters of Lake Xyasu 

 during Quaternary times, for a distance of about 15 miles. 



(b) The Permo-Carboniferous shells of Nkana are of importance 



in joining up areas of similar age on the north-western side 

 of Lake jNyasa ; as, for instance, Maramura with Xkana, and 

 the latter with the Kivera and Songwe-River regions (Kan- 

 dete Bach, etc.) of German East Africa, where Dr. Bornhardt 

 has recognized coal-bearing rocks with plant-remains 

 (described by H. Potonie), which he refers to the Karroo 

 formation. 4 



i Geol. Mag. 1891, p. 53. 2 Ibid. 1905, pp. 50-52 & pi. ii. 



3 Ibid. 1878, p. 100 & pi. iii, fig. 1. 



4 'Deutsch-Ost-Afrika' vol. vii (1900) pp. 495. 501 & geol. map No. 4. 



