Notes on a Few Silurian Fossils from Ayrshire. 175 



CLASS GASTEKOPODA. 

 Genus Bellerophon— Z>e Montfort, 1808. 



(Concli. Systematiqiie, i., p. 51.) 



BelleropJion expansus, J. de C. Sowerby. 



B. expansus, Sow. Sil. Syst., 1839, p. 613, t. 5, £ 32. 



B. expansus, Sow. " Siluria," 4th ed. 1867, t. 25, f. 8. 



Ohs. — There is a shell in Mrs Gray's collection possessing 

 all the characters of the above species, except that it is more 

 arched along the median line ; but this, I think, arises some- 

 what from distortion. The general outline, sinus and concen- 

 tric striae are well and distinctly marked. 



Zoc. and ^orito??..— Balcletchie, south-east of Girvan, in 

 rocks of Silurian age ; exact horizon uncertain. 



Belleroijlwn, sp. nov. (?). 



(Compare B. svMecussatus, M'Coy. Brit. Pal. Foss., p. 

 311, t. 1, L. f. 25). 



Ols. — In describing his B. suhdecussatus, Professor M'Coy 

 called attention to its close resemblance to the carboniferous 

 B. decussatus, Flem. I would on the present occasion follow 

 Professor M'Coy's example by pointing out the similarity of 

 the present form to another carboniferous species,^. JJrei,'Flem., 

 in the large, well-defined band and spiral stria3 ; the latter, 

 however, are finer and more numerous than is usually seen in 

 B. Urei, and there are indications of transverse striae, which 

 do not exist in the carboniferous species. Amongst Silu- 

 rian forms, the Drummuck examples are perhaps nearest to 

 B: suhdecussatus, M'Coy, but they differ in the much larger 

 size, well-defined band, and stronger spiral striae ; both speci- 

 mens are only casts, and somewhat compressed downwards, so 

 their exact form is not to be altogether determined. There are 

 a few strong transverse and oblique fluctuations or undulations 

 on one of the specimens, in addition to the remains of the 

 transverse striae. In all iDrobability the discovery of perfect 

 specimens will prove their form to be a new species. As the 

 specimens are only casts, and not good ones, I refrain from 

 giving them a name. 



