374 CARBONIFEROUS LAMELLIBRANCHIATA. 



Antero-posteriorly . . . .50 mm. 



Dorso-ventrally . . . .35 mm. 



From side to side . . . . 30 mm. 



Localities. — England : the Carboniferous Limestone of Thorpe Cloud, 

 Derbyshire. Scotland : the Lower Limestone series of High Blantyre. Ireland : 

 the Carboniferous Limestone of Tomdeely and Lisbane, co. Limerick. 



Observations. — This species was founded in 1842 by de Koninck upon a single 

 specimen from Tournay {op. cit.), and was re-described by him in his later work 

 as Ghsenomya Om.aliana. The figures in neither work are particularly good, but 

 the description is very accurate, and much fuller than it was his custom to give. 

 De Koninck draws attention to the resemblance between his shell and the 

 S. variabilis of M'Coy ; the differences between the two he quite appreciates. 

 I cannot, however, agree with de Koninck that the Allorisma Hamiltonensis of 

 Shumard and the Grammysia Hannibalis of Meek are the same species as the 

 Belgian shell. I have been able to compare specimens, and can see no reason for 

 mistaking the two forms, which in my opinion are quite distinct. The American 

 shell is much less gibbose, regularly ovate, compressed, and much smaller. The 

 concentric ribs do not bifurcate, and are fewer and larger ; the dorsal slope is 

 much smaller and more compressed ; but there is no doubt that both species 

 belong to the same genus. I think that de Koninck was most probably correct 

 in placing the Pholadomya transversa and Panopsea gravida of de Ryckholt as 

 synonyms of his shell. The curious surface markings of this species, though 

 much exaggerated, are well seen in the drawing of the latter shell, which was (de 

 Koninck states) an internal cast ; and the type specimen is still extant and 

 preserved in the Royal Museum of Natural History at Brussels. The figure 

 given by Baily is a good one, and I beheve that PI. XL, fig. 21, is the 

 specimen which served for the drawing. It was said to be from Lisbane, and to 

 be preserved in the Museum of the Geological Survey of Ireland, and this is the 

 case with the specimen here figured. 



De Koninck has described as Sanguinolites Omalii a shell figured as Solenopsts 

 Omalii, de Ryckholt. This is perfectly distinct from the species under discussion ; 

 and, if it is still retained in the genus, must have its specific name changed. 

 The shape of the shell, having a very narrow and produced posterior end, is 

 peculiar, and further examination may show that its generic characters differ 

 from those of Sanguinolites in other particulars. 8. Omalianus belongs to 

 that group of the genus which contains 8. costellatus and 8. variabilis, from 

 both of which it differs in important details. In gibbosity 8. Omalianus is less 

 strongly convex than the former, but more convex than the latter ; the rugae and 

 sulci are much stronger and fewer than in both. 



