42 Proceedings of the Royal Physical Society. 



more, certain varieties are peculiar to certain horizons, the 

 best example of this being, perhaps, a variety near aS^. 

 moscjiiensis (Fischer), which is found in the shale overlying 

 the cement limestone at Orchard quarry, near Glasgow, 

 and nowhere else. Another species, which well displays the 

 varietal tendency of Brachiopoda, is Producius semireticulatus, 

 of which three or four well-marked varieties are present in the 

 Carboniferous rocks of Scotland. 



Perhaps one of the best examples of the continuity of a 

 species throughout the Palseozoic rocks is exemplified by 

 Strophomena rJiomhoidalis (Wahl.). This shell is first met 

 with in British strata in the Caradoc, passes upwards through 

 the Devonian, and terminates its life-range in the Carbonifer- 

 ous, where it is represented by the variety analoga (PhilL). 

 The identity of this species throughout this great vertical 

 thickness of strata was first pointed out by Professor L. G. 

 de Koninck.* Its geological range is only equalled by its 

 geographical distribution, for we have the same shell of one 

 variety or another from the British, Continental, American, 

 and Australian Palaeozoic rocks. 



As an example of the geographical distribution of a Car- 

 boniferous Brachiopod found in Scotland, of large size and 

 common occurrence, we may cite Streptorhynchus crenistria 

 (PhilL). It has been met with at a similar horizon in India, 

 America, and Australia, and what is of especial interest the 

 most peculiar variety senilis has lately been found by Mr 

 R. L. Jack in the uppermost Carboniferous (perhaps Permo- 

 Carboniferous) deposits of Queensland.^ 



We have already referred to the dwarfed nature of the 

 Scotch Brachiopoda generally. Some species, however, do 

 not conform to this, notably many Producti and Streptorhyn- 

 chus crenistria. The former has been known to reach a size 

 of 5|- inches by 9 or 10 in width, and in the English lime- 

 stones somewhat larger. .| The first mention of this shell we 

 know of is by Ure,§ who refers to it as one of his Anomiw 

 echinatcc. He states, " The specimens are 5 or 6 inches in 



* IJech. Foss. Terr. Carb., Belgiqno, p. 215. 



t Ktlioridge, Proe. Hoy. Pliys. Soc, Ediiib., 1880, p. 282. 



X Davidson, Geologist, iii., p. 107. § History of Kutliergloii, p. 316. 



