196 BRITISH CARBONIFEROUS BRACHIOPODA. 



In Ireland it is mentioned from the limestone of Millecent, in Kildare. No Scottish 

 specimen has hitherto been discovered. 



Crania? trigonalis, M'Coy. PI. XLVIII, fig. 14. 



Orbicula trigonalis, M'Coy. Synopsis of the Carb. Foss. of Ireland, pi. xx, fig. 2, 



1844. 



Spec. Char. " Conical, obovate, trigonal ; anterior end narrow, rounded ; posterior 

 sub-truncate ; surface irregular, marked with close, rounded, radiating ridges from 

 the beak, which is small, deflexed, and little more than one fourth the length from 

 the anterior margin. Length four and a half lines, width three lines." (' Synopsis,' p. 104.) 



Obs. I have reproduced Prof. M'Coy's description, as I know so little about the 

 shell, a single valve having been hitherto discovered, and which was kindly lent me by Sir R. 

 Griffith ; and although I would not dare to assert that it positively belongs to the genus 

 Crania, it appears to me more probably so than to Discina, where placed by the author 

 of the 'Synopsis.' C? trigonalis was obtained from the Calciferous slate of Lisnapaste, in 

 Ireland. 



Family— DISCINIDyE. 

 Genus — Discina, Lamarck, 1819. 



The shells belonging to this genus are usually circular or longitudinally oval, the 

 larger or imperforated valve being conical, or limpet-like, with the apex inclining towards 

 the posterior margin. The lower valve is conical, opercular, flat, or partly convex, and 

 perforated by a narrow, oval, longitudinal slit, which reaches to near the posterior margin, 

 and which in recent species is placed in the middle of a depressed disc, the shell being 

 always attached to marine bodies by means of a pedicle, and never by the substance of the 

 shell, as in Crania. The valves are unarticnlated, and kept in place by a particular disposi- 

 tion of muscles, the occlusor and divaricator impressions being somewhat similarly situated 

 to those of Crania. Much has still to be done before the animal will have been completely 

 or satisfactorily anatomically investigated. The so-termed oral arms have been described 

 by Mr. S. P. Woodward, in his excellent ' Manual,' as being curved backwards, returning 

 upon themselves, and ending in small spires, directed downwards towards the ventral valve, 

 and the only process which could possibly have afforded support to the arms is developed 

 from the centre of the ventral valve, as in Crania. In recent species the shell is stated by Dr. 

 Carpenter to be horny and minutely punctate, the tub ul i being generally arranged in fasciculi, 

 so that their transverse sections present a series of dots. Dr. Gratiolet believes, however, that 

 the shell is not entirely composed of a horny substance, but somewhat similar to that of 



