CONOCARDTUM DECtJSSATUM. 471 



different form, and has no shelly expansion or flange. A small example of G. 

 Hibernicnm possesses the typical shape and other characters of the adult. 



I am very doubtful whether G. Eibernicum had a rostrum of any length. I 

 have examined several specimens which are adherent to the fringe, and where the 

 matrix in the neighbourhood has been undisturbed, but I have been able in no 

 case to see any indication of such a structure. 



An examination of the type of Phillips's PleurorJiynchns trigonalis demonstrates 

 at once that this specimen is the young of G. Eibernicum, and the species must 

 therefore be placed in the list of synonyms of the latter shell. The name G. 

 trigonale has, however, been given to a very peculiarly shaped shell, quite distinct 

 from C. Eibernicum, and de Koniuck has referred a series of shells from the 

 Carboniferous Limestone of Belgium to this species. It is now, therefore, necessary 

 to adopt a new name for these shells, which are at once separated from C 

 Eibernicum by the absence of the broad flattened posterior surface, by the more 

 median angular keel, and by the very narrow and compressed anterior wing, for 

 which I have adopted the name G. alatnm, de Koninck. 



Phillips's shell is said to have come from Bolland. 



The small shell figured by M'Ooy as Pleurorhi/nchus nodulosus is probably only 

 a young example of G. Eibernicu.m. I reproduce it, PI. LIU, fig. 6. It is very 

 vague and not free from the matrix, and the special characters on which M'Coy 

 founded the species are difficult to appreciate. I am inclined to regard the so- 

 called nodules as being due to somewhat accentuated lines of growth passing over 

 the angular margin of the valve. 



CoNOOARDiUM DEOUSSATUM, B. Ethevidge, jun., 1873. PI. LIU, figs. 1, 2, and 4. 



CONOCAEDIUM DECUSSATUM, E. Etlwridge, jun., 1873. Geo). Mag., dec. 1, vol. x, 



p. 297, pi. xii, fig. 5. 

 — — B. Etheridge, sen. Brit. Foss., pt. 1, PalEeozoic, 



p. 281. 



Specific Gharacters. — Shell almost equilateral, deep, compressed at either end, 

 gibbose in the median or body portion, broadly U-shaped. The anterior end is 

 compressed, short, deep, and truncate ; its margin descends downwards, and only 

 slightly backwards, and passing round into the inferior border becomes very 

 convex, then passes upwards again, and becomes continuous with the posterior 

 margin, forming one regular curve. The posterior end is triangular and much 

 compressed, forming a small wing. The body of the valve is convex from before 

 backwards, the passage from the body to the posterior flattened slope being more 

 sudden than that from the body to the anterior part of the shell. The hinge-line 



