260 R. Etheridge, jun.—Carboniferous Tubicolar Annelida. 
the Penneystone Jronstone of the Coalbrookdale Coal-field, has all 
the appearance of S. ambiguus. 
Loc. and Horizon.—Cults Lime Works, near Pitlessie, Fife, on the 
valves of Myalina crassa, Fleming; Roscobie Quarry, near Dun- 
fermline, Fife; Skateraw Quarry, near Dunbar; Gilmerton Old 
Quarry, near Edinburgh ; Galabraes and North Mine Quarries, near 
Bathgate, all horizons in the Lower Carboniferous Limestone group. 
Shore, east of Ravenscraig Castle, Pathhead, Fife, in shale of the 
Upper Carboniferous Limestone group (Mr. J. Bennie). 
3. Spirorbis helicteres, Salter. (Plate VII. Figs. 12-15.) 
8. helicteres (Salter), Rev. T. Brown, Trans. R. Soc. Edinb. 1861, xxii. p. 401, f. 3. 
Salter, Mem. Geol. Survey Scot., No. 32, 1861, p. 144 (without 
description). 
Young, Proc. Nat. Hist. Soc. Glasgow, 1878, ili. pt. 3, p. 329. 
Bigsby, Thes. Dev.-Carbonif. 1878, p. 243 (ibid). 
Etheridge, jun., Quart. Journ. Geol. Soc. 1878, xxxiv. pt. 1, pp. 4 and 
22 (ibid). 
Sp. char.—Tube forming on open helix, whorls laterally com- 
pressed ; as a rule the first two only are compact and discoid, the 
remainder being elongately extended, twisted, and often a quarter of 
an inch in length; aperture oval, with a plain thin margin; surface 
non-striate, but marked with irregularly-wrinkled ruge; habit 
unattached, gregarious. 
Obs.—The original description of this species was furnished by 
the late Mr. J. W. Salter for the Rev. T. Brown’s paper, ‘On the 
Mountain Limestone and L. Carboniferous Rocks of the Fifeshire 
Coast, ete.,” and was drawn up from specimens discovered by Mr. 
Brown. 
The extended portion of the tube sometimes turns or twists upon 
itself, in an open elongated and loose helix, at others it curves about 
in an irregular manner. S. helicteres appears to be quite unattached 
to any foreign body, this character being alluded to by Mr. Salter 
in the following words: “It occurs in distinct beds, hundreds 
grouped together, yet without ostensible attachment to any other 
object than its own species.” Mr. Salter considered Sp. helicteres to 
be allied to Serpula Archimedis, de Kon.;! the latter is, however, less 
compressed, more closely coiled, and has close-set striz and large 
transverse plaits. Both Spirorbis caperatus, M‘Coy, and Serpula 
carbonaria, Binney, terminate in free tubes, more or less coiled; but 
the former, at any rate, is easily to be distinguished from the present 
species, although it would be well to make a comparison between 
Mr. Binney’s form and the latter; I think they will be found to 
approach one another very closely, although the free tube of Serpula 
ass Binney, does not appear to be at all tortuous, or bent on 
itself. 
Unless seen in mass on the weathered surfaces of hand specimens 
of limestone, when its peculiar characters become at once apparent, 
it 1s, at times, difficult to distinguish Sp. helicteres from S. pusillus. 
The coiled portions of both are much alike at first sight—both 
1 Descrip. des Anim. Foss. p. 57, t. G. f. 6. 
