Fossils from the Hindu Khoosh. 55 



The figured specimen conforms pretty well to the diagnosis given 

 by Davidson, which at least should confirm the view that this shell 

 is a species of Athjris. The following especially applies to our 

 specimen : — " Beak tumid, moderately produced, incurved and 

 truncated by a small circular aperture close to the umbone of the 

 opposite valve ; surface more or less deeply marked by numerous 

 close, concentric, regular, imbricating lamina of growth." In our 

 shell there is just enough left of these imbricating laminee in the 

 sulcus of the ventral valve to show what the ornaments of the shell 

 originally were. 



There are three specimens in the collection, but this is the only 

 one showing the concentric ornamentation. 



9. Athybis, species or variety. (PI. Ill, Figs. 3a-c.) 



This is a very strongly marked form, and might in some sense 

 be described as an exaggerated variety of A. concentrica. The 

 features of that species, such as the sinus on the ventral valve and 

 the mesial fold on the dorsal valve, as likewise the imbricating 

 concentric ornamentation, are intensified. The principal difference 

 consists in the great predominance of the ventral valve in the region 

 of the beak, almost recalling the outline of Pentamerus. 



There is one specimen, in by no means a bad state of preservation. 



Genus ATEYPA. 



Nearly half the Brachiopoda in General McMahon's collection 

 belong to this genus, and the specimens are for the most part free 

 from matrix, whilst some are fairly well preserved. There is 

 considerable uniformity as to size and shape, and the ornaments, 

 as a rule, are strongly imbricated. Hardly any of the specimens 

 present the fine lines of Atrypa reticularis, and moreover the 

 prevailing shape is too circular for that species. The Chitral fossils 

 more nearly approach Atrypa aspera and its numerous varieties, 

 and under this species it will be convenient to focus the whole group. 



10. Atrypa ASPERA, Schlotheim. (PI. Ill, Figs. 4, 5a, h, 6a, h, la, h.) 



Atrypa aspeta, SchJotheim : Brit. Dev. Brach., p. 57, pi. x, figs. 5, 6. 

 IMd., yar. squamosa, Sow. : Brit. Dev. Brach., p. 57, pi. x, figs. 7, 8. 

 Ibid., var. Sinensis, Kayser : Richthofen's China, Bd. iv, p. 83, pi. ix, fig. 3. 



Davidson classified Atrypa aspera simply as a variety of 

 A. reticularis, and he further remarks that it is always found in 

 the same beds and localities where the latter occurs and abounds. 

 The important point for us to consider is the fact that, whereas 

 A. reticularis is equally abundant in the Upper Silurian and 

 Devonian, A. aspera, be it species or variety, occurs mainly in 

 the Devonian, its place in the Upper Silurian being occupied by 

 A. imbricata, Sow. As to the existence of intermediate forms, no 

 doubt the affinity of every variety of Atrypa may be traced to the 

 prevailing form, viz. reticularis, if one is so inclined. 



In dealing with the Chitral fossils. Fig. 5a may be accepted as 

 an average specimen, very well preserved as regards ornaments, but 



