170 SYNOPSIS OF THE CHARACTERS OF THE 



Spirorbis minutus. Portk. 



Spirorbis minutus. Portk. Geol. Eep. 



I have not seen good specimens of this sliell ; those on the specimens of Dithyrocaris Colei which I have 

 examined, being very indistinct ; it seems, however, a very good species. I have not seen it except in this situ- 

 ation. There are only about two turns in the spire : diameter about one-fifth of a line. 



Spirorbis omphalodes. Gold. ? 



Serpula omphalodes. Gold. Pet. ? 

 On certain shale-plants are found abundance of a little shell referred by Captain Portlock to the above 

 species. The Irish specimens are perfectly flat on the attached side, smooth, and having two and a half or three 

 turns in the spire ; the mouth semicircular. Goldfuss's characters do not exactly agree with those, I have therefore 

 marked the reference with a doubt. 



Spiroglyphus. Lam. 



Gen. Ch. — Discoid; spirally coiled; parasitic; forming a deep groove for itself in the surface of shells. 



Spiroglyphus marginatus. M'Coy. (PL XXIII. fig. 27). 



Sp. Ch. — Discoid; volutions hardly two; vipper side rounded; attached side flat; externally bordered by 

 a broad, flat keel ; surface smooth. Parasitic on various shells in one or two localities. 



Serpulites carbonapuus. M'Coy. (PI. XXIII. fig. 32). 



Sp. Ch. — Tube small, narrow, shelly; terminating posteriorly by two lengthened, cylindrical tubes, the 

 prolongation of the lateral, thickened ridges. 



This remarkable species is intermediate in the texture of its tube, between the S. lonc/issirmis, Sow., and 

 S. membranaceus, M'Coy, being more delicate than the former, but much more testaceous than the latter ; it 

 is, however, greatly inferior to either of them in size, the most usual diameter of the compressed tube being one 

 or one and a half lines, and the largest specimen which has, as yet, fallen under my observation was barely two 

 lines in width ; the forked, posterior termination is a new and important character, which, however, I believe 

 to belong to the whole genus, rather than to characterize the present species. It is formed of two long testaceous 

 tubes, bordered on the inside of their base by a membranous prolongation of the principal tube. 



My friend. Dr. Scouler, has recently shewn me specimens of this species, collected by himself, from the 

 Scotch carboniferous shale. 



Serpulites membranaceus. M'Coy. (PI. XXIII. fig. .31). 



Sp. Ch. — Tube elongate, curved, membranaceous; abdominal and dorsal (?) margins thickened. 



The extraordinary genus Serpulites, hitherto thought so characteristic of the Silurian rocks, as to distin- 

 guish the slates of that period from those of the carboniferous system, has recently occurred in some abundance in 

 the shales of the carboniferous period ; the species, however, appear to be distinct from those in the Silurian rocks. 

 The present species is of great size, probably exceeding that of the S. loitt/issimus ; its substance, however, instead 

 of being decidedly shelly as in that fossil, is excessively thin and membranous, so that the smallest fragments 

 of the two species could be easily discriminated. A very interesting fact is shewn by our figure, namely, that 

 two opposite points of the circumference of the tube were really thickened, forming two opposite, longitudinal 

 ridges (or tubes ?) and that this appearance is not due to pressure. General width of the compressed tube seven 

 lines. 



