204 DE. F. J. NOBTH OS [vol. lxxvL 



of Wales. Other examples, from Settle, are on a tablet numbered 

 501 in the Sedgwick Museum, Cambridge. 



Horizon and localities. — Upper Dihunopliyllum Zone 

 (D 2 -D 3 ). Principal Sibly reports it as being characteristic but rare 

 in D 3 in Derbyshire and North Staffordshire, 1 while in Ireland it is 

 characteristic of the Gyathaxonia Beds (D s ) at Rush 2 ; Martin's- 

 figured specimen was recorded as from Middleton (Derbyshire). 

 A number of specimens from the neighbourhood of Settle are in 

 the Sedgwick Museum. 



Remarks. — In the original description of ' A. subconicus,' 1 

 Martin compared this species with his ' Anomites cuspidatiisj from 

 which it differed in having fewer and more angular ribs, and a flat 

 area. He said that, in the shape of its area, it was intermediate 

 between that species and another undescribed form with a more in- 

 curved area ; this form was, in all probability, Tylothyris laminosa. 

 Davidson expressed a doubt as to whether Martin's species was only 

 an exceptional variety of S. cuspidata, and reproduced Martin's 

 figures. 3 In his appendix to the ' Carboniferous Brachiopoda,' 

 Davidson figured a testaceous specimen of T. suhconica in which the 

 lamellose ornament was perfectly preserved, and admitted its specific 

 distinction from S. cuspidata, but compared it to S. laminosa. 



De Koninck stated that the lamellar ornament occurred in young 

 shells only, 4 and was absent or scarcely visible on adult specimens ; 

 but that author, owing no doubt to the state of preservation of his 

 material, apparently regarded Oyrtina septosa (Phillips) as the 

 adult form of T. suhconica, for the form which he figures as the 

 latter species is certainly O. septosa. 



The lamellar ornamentation is not often preserved ; in ex- 

 foliated specimens the costse are smooth, and appear more rounded 

 than in perfect shells. 



Tylothyris stjbcchstca CxYStletonexsis, subsp. now (Text- 

 fig. 4 d, p. 199 ; PL XIII, figs. 3, 4 a & 4 b.) 



This form differs from T. suhconica suhconica in the following* 

 respects: — The shell is rather less transverse, and the cardinal 

 extremities are blunter, being practically right angles. The costse 

 are stronger, less angular, and towards the cardinal extremities 

 are less clearly defined than in the other subspecies. The sinus is 

 shallower and less angular, and the line along its floor more strongly 

 curved than in T. suhconica. The area is more or less concave, 

 and terminates in a small, incurved, pointed beak (see fig. 4 d, 

 p. 199). 



1 Sibly [31]'p. 51. 



2 Vaughan [34] pi. xxx, fig - . 7. 



:! Davidson [4] p. 48 & pi. ix, figs. 3, 3 a, 3b. These figures were apparently 

 copied on the stone directly from Martin's drawings, and are therefore reversed. 



4 De Koninck [19] p. 255 & pi. xii bis, figs. 5 a-5 c. (Really figs. 4 a-4 e, 

 although in the text, as well as in the explanation of the plate, he cites them 

 as 5 a-5 c ; fig. 5 is a species of Chonetes.) 



