40 Proceedings of the Royal Physical Society. 



in the limestones and shales of the East, but the number of 

 species is less.* The latest computation places these at from 

 fifty-three to fifty-four. The district which appears to have 

 yielded the greatest number and variety of Brachiopoda in 

 Scotland is that of Campsie, where forty-three have been 

 found.-t* Brachiopoda often appear to be the first to make 

 their appearance in any given series of strata, if we may judge 

 by the position of their remains in the beds in which they 

 are found ; equally so they are one of the latest classes to 

 disappear in point of time. As an illustration of this we 

 may adduce the case of Piscina nitida (Phill.). A variety 

 of this shell occurs in abundance low down in the Calci- 

 ferous Sandstone series, in a marine band in the Wardie 

 shales, at Woodhall, on the Water of Leith. % The same 

 species is one of the shells met with in brown ironstone 

 nodules some 60 fathoms above the Ell coal in the true Coal 

 Measures, and not far from the top of the Carboniferous 

 system in Scotland. § 



The abundance or rarity of Brachiopoda appears to be quite 

 a local matter, and to follow no general rule. Either of 

 these phenomena is probably due to suitable or unsuitable 

 deposits acting as a sea bottom, food, temperature, and cur- 

 rents. In some parts of Lanarkshire, for instance, the genus 

 Productus so outnumbers every other form of Mollusca in 

 certain beds of the Lower Limestone Group, as to confer on 

 them the name of the so-and-so Productus limestones, accord- 

 ing to the species represented therein. Beds of coral (of the 

 genus Litliostrotion, etc.) seem to have abounded in Brachio- 

 pod life. For instance, at Aberlady Bay, Haddingtonshire, 

 portions of the beach are wholly composed of such a reef 

 teeming with two species in particular, Athyris amhigua 

 and Eliynclionella pleurodon. In the Upper Limestone 

 Group, one of the lowermost limestones, known as the Index, 

 is in a great measure composed of the remains of Productus 



* Somervail, Trans. Geol. Soc, Edinb., 1877, p. 97. 



t Young, " On the various Genera and Species of Bracbiopod Sbells found 

 in tbe Main Limestone of the Campsie Valley " (Trans, Glasgow Nat, Hist. 

 Soc, 1864, i,, p, 95). 



X Etheridge, Quart. Jour. Geol. Soc., 1878, xxxiv., p. 24, 



§ Skipsey, Trans. Glasgow Geol. Soc, ii,, 1865, pt. 1, p. 52. 



