122 CARBONICOLA, ANTHRACOMYA, AND NAIAD1TES. 



Unios, which was not mentioned by name, Phillips says, " Williamson has inaccu- 

 rately referred this shell to Unio nuciformis" [of Hibbert]. The second Unio is 

 named Unio linguiformis = Unio Phillipsii, Williamson, although no grounds are 

 given for this apparently arbitrary change of name, in spite of a description, though 

 meagre, having been published, part of which I have quoted above. It is to 

 be noted that Mr. R. Etheridge, in his redescription of this species (op. supra 

 cit.), adds " without description " to his reference to Williamson's original 

 publication : quoting him, I fell into the same error in my former paper. 



Williamson only describes one shell, but mentions later in his paper remains 

 which had been mistaken for fish scales, measuring about a quarter of an inch 

 across. But it is the shell which he refers to Unio nuciformis and calls Unio 

 Phillipsii. Moreover this species cannot be said to have a " hinge-line (which) 

 deviates very little from parallelism to the front lines of growth." Indeed, 

 Phillips's first Unio shell appears from the description to correspond better with 

 Williamson's form. Neither Professor Rupert Jones nor Mr. R. Etheridge, jun., 

 noticed this curious mistake of Professor Phillips, both authors giving Unio 

 linguiformis as a synonym of Anthracomya Phillipsii. 



The original specimen being that of a shell crushed flat, it is difficult to judge 

 what exactly would be the form of uncrushed examples. I have referred fairly 

 perfect shells from the horizon of the Knowles ironstone to this species, PI. XVI, 

 figs. 11 — 13, one of which (fig. 11) is a cast, and the exact outline of the shell cannot 

 be seen on account of imperfections of the extreme anterior portion and the 

 posterior border. The others (figs. 12 and 13) would, I think, if crushed flat, 

 exhibit a similar form to those of A. Phillipsii, which occur in such numbers in 

 the higher beds. 



If I am correct in my reference, A. Phillipsii was a fairly tumid shell, so gently 

 tumid that the diagonal ridge so characteristic of the genus is not apparent ; and 

 this view is supported by an observation by Mr. E. W. Binney, that in the 

 uncrushed state the shell closely resembles a Modiola. This is so, speaking broadly, 

 but the position and shape of the umbones are characteristically different from 

 that which obtains in Modiola. I have recently obtained both crushed and 

 uncrushed specimens of this species from the Speedwell pit, Gloucestershire. In 

 these shells the oblique ridge is more acute, and not so gradually gibbose as in the 

 forms from the Knowles [ronstone, Fenton. 



The shell seems to occur at several horizons in the Bristol district, judging 

 Prom the matrix in which they occur, but I am unable to give the exact beds. 

 This is, 1 believe, ;i new discovery (the shells were collected by Mr. Stock, of 

 Bristol), and an interesting one, as molluscan remains are very rare indeed in this 

 coal-field. 



In crushed examples it is often very hard to distinguish between Anthracomya 



