94 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



narrow, V-shaped trench between the opposing valves, the continuation of the 

 slight groove along the border of the shell which gives attachment to the external 

 ligament. 



Dimensions. — The type-specimen (PI. XIII, fig. 4) measures — 



Antero-posteriorly. Dorso-ventrally. From side to side. 



48 mm. (restored) 29 mm. (near posterior end). 20 mm. 



Fig. 5, PI. XIII, 51 mm. 32 mm. 23 mm. 



Localities. — Pennystone beds, Coalbrookdale. Little Mine (Burnwood) 

 Ironstone, North Staffordshire. Black Mine Middle Coal-measures, Oldham, 

 Lancashire. 



Observations. — This species was one of the two members of the genus first 

 described and figured, and I am fortunately able to refigure the original 

 specimen through the kindness of Professor Prestwich, who has lent me the fossil 

 for examination. The anterior end is absent, a fact which was shown in the 

 original drawing by James de Carle Sowerby (op. supra cit.), the lines of growth 

 anteriorly ending abruptly, although this incompleteness was not noted in the 

 description, where it is stated, " Anterior side small, rounded ; . . . . beaks near 

 the anterior side." Mr. Salter, judging hastily from the figure alone, says in his 

 original description of the genus Anthracomya, " A. dolabrata (Sow.) is still 

 more convex [than A. Adamsii], and has an almost obsolete anterior side " (op. 

 supra cit.). 



Anthracomya dolabrata is very closely allied indeed to A. Adamsii, and in North 

 Staffordshire the two species are found together in the Burnwood Ironstone. 

 On the other hand, there is a strong resemblance to certain large forms of A. 

 modiolaris, so that it forms a connecting link between these species. 



From A. Adamsii, Anthracomya dolabrata differs in its much greater convexity, 

 being the most gibbose species of this genus, by the greater tumidity and height 

 of the umboncs. The greatest thickness is subumbonal, not as in A. Adamsii about 

 the centre of the shell ; and relatively the antero-posterior measurement is greater 

 than in A. Adamsii. But forms occur intermediate in shape and character between 

 the two, — for example, fig. 6, PI. XIII. 



I have seen nothing in Continental museums which can be considered at all 

 like the species under description ; and, indeed, the shell has been very little 

 noticed by paleontologists. Salter dismisses it in one line, and Captain Brown 

 simply copied Sowerby's figure, giving a very inaccurate description, and stating 

 the locality as Coalbrookdale. It is very evident that he never saw any specimen 

 of 1 he shell in question. 



In my paper " On the Affinities of Anthracoptera and Anthracomya" (' Quart. 

 Journ. Geol. Soc.,' vol. xlix, p. 2C>1) I re-described the species from the type 

 kindly lenl for that purpose by Prof. Prestwich, and I then stated that certain 



