ANTHRACOMYA MINIMA; Var. 119 



13*. Antheacomya minima, var. carinata. Plate XVI, figs. 35 — 39. 



Non Antheacomta carinata (pars), Hind. Quart. Journ. Geol. Soc, vol. xlix, 1893, 



p. 273, pi. x, figs. 1(5, 16 a. 



General Characters. — Very much produced transversely, anterior end very 

 small and almost obsolete, bluntly rounded, sloping- rapidly into the inferior border, 

 which is so slightly convex as to appear almost straight. The posterior part is 

 produced, forming about seven-eighths of the shell, with a strong oblique ridge 

 passing downwards and backwards to the inferior border at the junction of the 

 third and posterior fourth of its extent, when it becomes lost on the surface of the 

 shell. Anterior to the ridge the shell is sinuated and flattened, and very rapidly 

 compressed into the lower border. Above the ridge the shell is also rapidly 

 compressed into the superior border. The posterior border is curved elliptically. 



The hinge-line is straight, equalling about three-fourths of the length of 

 the shell in measurement. The umbones are situated very anteriorly, tumid, 

 and small. 



The exterior is covered with fine strias and lines of growth, which, starting 

 from the anterior end, become curved upwards as they reach the oblique swelling, 

 and are reflected up to the superior border. Periostracum thick and wrinkled. 



Interior not seen. 



Dimensions. — Fig. 39, PI. XVI, measures — 



Antero-posteriorly . . . .22 mm. 



Dorso-ventrally (at posterior end) . . 8 mm. 



Laterally . . • • .7 mm. 



Localities. — From an ironstone band on the Middle Coal-measures of Lancashire 

 at Prestolee. The Knowles Ironstone bands, North Staffordshire Coal-field. 



Remarks. — The specimen I first described I now find to have greater affinity 

 with A.pumila, Salter; and, moreover, it comes from the locality of Salter's type. 

 I had neither seen the series of shells from the South Wales Coal-field in the 

 Cardiff Museum, nor the intermediate forms which connect A. carinata with 

 A. minima. I have now found them in the beds both in Lancasbire and North 

 Staffordshire which contain this shell, but owing to the differences in form and 

 size, and the comparative rarity of this variety, I have still retained the name 

 carinata, but as a varietal form of A. mini ma. The chief difference which marks 

 off this variety is in the very rapid and excessive growth of the posterior end, and 

 the consequent throwing into greater relief the oblique ridge, which, instead of 

 being directed towards the inferior posterior angle, is left behind some distance 

 along the lower border. 



