186 DR. F. J. NORTH OX [vol. lxxvi, 



grit of similar age at Kendal. 1 Davidson figured it from Kendal. 2 

 The difference between these northern representatives of mut. 

 eacoleta and those from the South- Western Province is probably, in 

 part at least, explained by the fact that in the former area they 

 occur almost exclusively in oolitic and arenaceous deposits, while 

 in the latter they are usually found in the crinoidal and shelly 

 limestones. 



The peculiar variations of mut. exoleta found in the Waulsortian 

 knolls of Ireland have already been referred to. 



SyRINGOTHYRIS CTTSPIDATAmut. cuspidata. (Text-fig. 3y, p. 178; 

 PI. XI, figs. 7-8 & PI. XII, figs, la-2 b.) 



1796. Anomites cuspidatus Martin [22] p. 44 & pi. iii, figs. 1-4. 



1809. Conch yliolithus anomites cuspidatus Martin [23] pi. xlvi, figs. 3-4 & 



pi. xlvii, fig. 5. 

 1816. Spirifer cuspidatus J. de C. Sowerby [32] pi. cxx, fig. 3. 

 1836. Spirifera cuspidata Phillips [27] p. 216 & pi. ix, fig. 1. 

 1858. Spirifera cuspidata Davidson [4] pi. viii, figs. 21-24 & pi. ix, fig. 2. 

 1868. Spirifera cuspidata King [17] pis. ii-iii. 



This is the typical form of S. cuspidata represented by Martin's 

 ho lo type. Its distinguishing features are as follows : — Apical 

 angle about 90°, area rather more than half as high as wide, 

 nearly flat, but slightly reclined, and rounding over into the some- 

 what inflated lateral slopes; cardinal extremities rounded. Brachial 

 valve strongly convex, with a swollen beak well raised above the 

 level of the hinge-line. Costa? about sixteen on each lateral slope, 

 strong, depressed, separated by furrows wider and less numerous 

 than those in the earlier forms of S. cuspidata and in contemporary 

 examples of S. elonyata. Delthyrial supporting-plates nearly 

 parallel ; transverse plate thin ; syrinx perfectly developed, but 

 relatively small. 



The dimensions of an average specimen are as follows : — width 

 along hinge-line, 56 mm. ; length of brachial valve, 30 mm. ; 

 height of area, 32 mm. Very rarety the mutation is represented by 

 giant specimens measuring nearly 100 mm. in width. 



Horizon and localities. — This mutation occurs only in the 

 Dibunophyllum Zone, especially D 2 , and is represented in the Mid- 

 lands, in Yorkshire, and at Axton (Flintshire) ; and by the 

 distorted specimens from Cork, already mentioned on p. 181. 



(</) Pre-Carboniferous History of Syringotliyris. 



In this country and in Belgium, Syringotliyris first appears in 

 the Cleistopora Zone of the Carboniferous Limestone, with all its 

 essential characters fully developed ; but in neither of those areas do 

 the Devonian rocks yield any Spiriferid shells that can be regarded 

 as possible ancestors of Syringotliyris. 



An apical callosity and even a transverse plate are frequently 



1 A number of specimens are in the Sedgwick Museum, Tablet 639. 



2 Davidson's figures [4] pi. Iii, figs. 3 & 3 a, appear to be idealized, and to 

 combine the characters of 8. cuspidata and Tylothyris subconica. 



