470 CAllHONIFKllOUS LAMliLLIBRANCHIATA. 



Dlnienslo)is. — PI. LIII, fig. 10, a fairly complete specimen, measures — 

 Antero-posteriorly (not including the rostrum) . 45 mm. 



Dorso-ventrally . . . .48 mm. 



From side to side . . . .53 mm. 



PI. LIII, fig. 8— 



Dorso-ventrally . . . .54 mm. 



Depth of flange . . . .42 mm. 



Localities. — England: the Carboniferous Limestone of Withgill, Yorkshire; 

 Clitheroe, Lancashire; Thorpe Cloud, Derbyshire. Ireland: the Carboniferous 

 Limestone of St. Dooghlas and Malahide, co. Dublin ; Rowerby, Kilmallock, and 

 Kilo'roo'an, co. Limerick. 



Observations. — This species was figured twice in Sowerby's ' Mineral Con- 

 chology ' {op. cit.), the second time to show the peculiar flange in extension of the 

 keel, and on both occasions was referred to the genus Gardvmn. The first figure 

 is stated to be a compound one. Sowerby says, " I have had recourse to several 

 specimens to produce the upper figure," and there is no doubt that it represents 

 the species very well indeed; the specimens are in the Sowerby Collection at 

 the British Museum (Nat. Hist.). Phillips's figure unfortunately cannot be taken 

 as typical, for it is stated to be " reduced." There has been little or no miscon- 

 ception with regard to this species on the part of authors, with the exception that 

 M'Coy described a crushed example as a new species, PleurorJu/nchus gigantens, 

 the types of which are very much distorted and too imperfect to serve as types. I 

 have no doubt at all that the two shells figured as Fleurorhynchus giganteus are 

 large examples of Sowerby's species. M'Coy states that " the contracted posterior 

 end [is] marked with strong ridges from the beak." This observation, correct 

 as to the specimen itself, was not understood by its author, for the ribs are 

 seen only because the outer layer of shell has been removed — a fact that is at once 

 evident on an examination of the type specimen, PI. LIII, fig. 7. The other 

 specimen figured by M'Coy, a crushed fragment, however, shows the broad shell 

 flange attached to the angular keel. 



This species is popularly known to quarrymen by the name of asses' or horses' 

 hoofs, from the shape of the shell and the cast left from the posterior surface and 

 its flange. The very short, deep, rapidly expanded angular shape and flattened 

 posterior surface distinguish the shell at once from all other species. I am not 

 aware at present of any other British species having possessed a broad shelly process 

 or flange, but it is certainly present in the 0. suhtrigonale from the Upper Helderberg 

 group and an American form, which are quite distinct from G. Hihernicuw.. 



De Koninck, as he himself later on admitted, referred a totally different shell 

 to C. Hibernicum in 1842. The name G. Herculeum was substituted for it in 

 1885 (up. cit.). This species, as may be seen by PI. LI, fig. 11, has a very 



