CARBONIFEROUS BRACHIOPODA. 
291 
Strep, crenistria, var. robusta. Hall, with M'Co}''s type, I could not find between them 
any differential features. Mr. J. Thomson informs us, in his valuable paper, that the 
shell he has identified with liall's so termed Orthis robusta} " varies in size from a line 
and a half to an inch and a half across the hinge-area, and exhibits many features both 
in form and thickness. In some specimens the dorsal valve is deeply convex, and the 
ventral slightly concave ; some again are much thinner than others, and approach much 
closer to the condition of Streptoi'liynchus crenistria of Philhps. . . . Seldom, indeed, 
have I found this shell in our purer limestones. It almost invariably occurs in 
calcareous or arenaceous shale, clustering in colonies, thus showing that, while it was 
gregarious in habit, it dwelt at no great depth in the primeval seas." 
In a paper by Mr. James Neilson, jun., entitled " Geological Notes on the Cuttings 
in the City of Glasgow Union Railway, between Bellgrove and Springburn " (' Trans. 
Geol. Soc. Glasgow,' 1875), some internal casts are again referred to the variety robusta. 
Hall. Through the kindness of Mr. Neilson I have been able to examine and figure 
one of the specimens, which he states to be plentiful in a grey sandstone at the bottom 
of the Millstone-grit series, according to that geologist, possibly a passage-bed between 
the Millstone-grit and Upper Limestone series ; to this horizon Mr. J. Thomson is now 
of opinion the Tirfergus Glen deposit may be referable. The specimens came from the 
railway-cutting at from 20 to 200 yards south of Garngad Road, Glasgow, near the 
shale containing Producius carbonarius, which is probably only a few feet higher in the 
section. Mr. Neilson's specimens were of about the same dimensions, none exceeding one 
inch six lines in breadth by one inch three lines in length, being a much smaller shell 
than Hall's Orthis robusta. Mr. Neilson believes that it is the same shell, or variety 
of Streptorhynchus^ found by Mr. J. Thomson in the neighbourhood of Campbeltown, and 
I concur in his opinion. 
Genus Strophomena, Rajine-sque. 
31. Strophomena rhomboidalis, var. analoga, FMU. Dav., Carb. Mon., p. 119, 
PL XXVIII, figs. 1—13; 
Sup., PI. XXXVI, fig. 23. 
Mr. John Young informs me that examples of this shell show numerous, but rather 
widely placed, oblong perforations, that these occur amongst the vascular impressions as 
well as in other portions of the shell ; but, like those seen in most species of Froductus, 
1 " Report of the Geological Survey of the State of Iowa," vol. i, part 2, 'Palaeontology,' p. 713, 
pi. xxvii, fig. 5, 1858. 
38 
