134 BRITISH CARBONIFEROUS BRACHIOPODA 



Dimensions variable ; three examples have measured — 

 Length 15, width 16|, depth 5 lines. 

 » 15, „ 15, „ o ,, 



Obs. O. Michelini is a common and far-spread Carboniferous species, always recog- 

 nizable, and easily distinguished from O. resupinata and O. Keyserlingiana both by external 

 shape and by interior differences, which last are evinced in the narrowness of the median 

 ridge, and less inclined slope of the adductor or occlusor muscular impressions ; while in the 

 dorsal valve the space occupied by the adductor, divaricator, and ventral adjustor muscles 

 is wider than in 0. resupinata. There is also a singular impression, marked N in 

 fig. 9, which is with some uncertainty attributed by Mr. Hancock to the pedicle muscle. 

 The striation in 0. Michelini differs also from that of 0. resupinata and O. Keyserlingiana 

 by the absence of that peculiar dilatation of some of the striae before the occurrence of a 

 spine-like projection, and the remarkable abrupt diminution of the swollen ridge beyond 

 the spine, which produces those elongated drop-like mark, so visible over the surface of 

 the last-named species. Professor De Koninck, who in 1843 first noticed the spiny 

 investment of the shell under description, expressed the opinion that the dorsal 

 valve was alone so adorned ; but a careful examination of many specimens has convinced 

 me that spines existed on both, although perhaps more numerously spread on the dorsal 

 valve. The spines were likewise more abundant on some examples than on others, 

 nor do they seem to have anywhere exceeded about a quarter of an inch in length. 



Ort/iis Michelini appears also to have varied less in shape than the preceding species ; 

 the shortness of the hinge-line is, however, in some specimens very remarkable. 



0. Michelini abounded where it occurred, and especially so in certain shales at the top 

 of the Mountain Limestone, such as at Clattering Dykes, on the middle ofMalham Moor, in 

 Yorkshire ; nor is it rare in the Mountain or Carboniferous Limestone of Settle, Bolland, 

 Fountain Fell, the Isle of Man, &c. 



In Ireland, it occurs in the Carboniferous Limestone and shales at Lisnapaste, Little 

 Island, Millecent, BallydufF, Bruckless, Malahide, Old Leighlin, &c. It may also be 

 collected by millions (in the condition of internal casts and impressions) in the calciferous 

 states of Bally seedy, County Kerry. 



In Scotland it is also very plentiful in certain localities, such as at Gateside, near 

 Beith, where detached valves occur by thousands in the same stratum of shale whence 

 David Ure collected his specimens of the species. 1 In Lanarkshire, it occurs at Langshaw 

 Burn, Brockley, and Middleholm, near Lesmahago, Auchentibber, Calderside, and Phillips- 

 hill, High Blantyre ; Capel Rig, East Kilbride, &c. In Renfrewshire, at Orchard Quarry 

 Thornliebank ; Barrwood and Howood, near Paisley. In Ayrshire, at Roughwood, West 

 Broadstone, and Treehorn, near Beith, &c. In Stirlingshire it is found in several stages ; 

 and occurs also in Dumbartonshire, Fifeshire, &c. 



1 David Ure appears to have been the first naturalist who figured this shell in Great Britain ; for figs. 13 

 and 14 of the fourteenth plate of the 'History of Rutherglen,' published in 1793, evidently belong to the 

 species under description. 



