Vol. 67.] THE CARBONIFEROUS SUCCESSION IN &OWBB, 569 



The structure of the columella appears, therefore, to be closely 

 similar to that of a Clisiophyllid, and, in particular, to that of 

 Carcinojjliyllwn : — the tall vaulted tabulae, each buttressed by 

 lamellae and crested by the mesial plate, are arranged in a series 

 of tents one below, and within, another. 



The close approximation of the descending portion of successive 

 tabular vaults forms a thick tubular wall enclosing the entire 

 central cylinder throughout the length of the coral. 



Comparison: — The specimen figured in the Rush Paper, and 

 cited above, was derived from the Cyathaxoaia Beds of Bradbourne 

 in Derbyshire ; similar forms, less well preserved, are common at 

 the same level at Rush. 



The structural plan is essentially similar to that of the Grower 

 specimens. 



By rubbing clown the Bradbourne specimen through a complete 

 tabular interval, it was demonstrated that the mesial plate is not 

 continuous through the tabulae, but that it starts afresh above 

 each tabula as a crest, and extends to the under surface of the 

 next tabula above; the lamellae apparently exhibit the same 

 phenomenon. The resemblance to the central structure of Clisio- 

 phyllids is, therefore, extremely close. 



Specific differences from the Go wer form are obvious : — In the 

 Bradbourne specimen there is a narrow peripheral ring of vesicles 

 and the lamellae are much stronger and more closely set than in 

 the Gower specimens. In both these characters there is a still 

 closer approach to structures characteristic of Carcinophyllum. 



(B) BRACHIOPODS. 

 PRODUCTIDS. 



Pro ductus. 



Producxus sulcatus Sow. (PI. XLI, figs. 1 a & 1 h.) 



Sowerby, c Min. Conch.' vol. iv (1823) pi. cccxix, tig. 2. 



The holotype of the species is preserved at the British Museum 

 (Natural History) in the Sowerby Collection ; it was obtained from 

 Derby. The same form is common in Yorkshire at the top of the 

 Carboniferous Limestone. 



The specimen here figured is from D 2 _ 3 of the Oystermouth 

 Quarry, where the species is not common. 



Description: — The pedicle-valve has the following striking 

 characters : — 



Form cylindrical and of quadrate cross-section. Umbonal region parallel 



to the marginal, and therefore invisible in a ' back view ' ; the two 



regions are united by a high vault. Strong reticulation on the umbonal 



region. Coarse, tall, marginal ribs separated by deep furrows (whence 



the specific name). Cylindrical wings strongly projecting, and each 



ornamented by two rows of spines, respectively along and oblique to 



the hinge-line. 



The holotype of Productus sulcatus Sow. has a shallow median 



sinus, whereas the Oystermouth specimen is merely flattened in 



the median region. 



