SPIRORBIS HETEROSTROPHUS. 419 
Occasionally the aperture is turned upward. All the specimens are small and of uniform 
size. 
Montagu (1803)! describes it as having ‘“‘a strong, spiral shell, of a dirty white colour, 
with two or three reverse volutions placed laterally, furnished with three longitudinal ridges, 
one along the back, and another on each side, roughly wrinkled transversely ; the base is 
flat and somewhat spreading ; aperture orbicular, and invariably placed opposite the sun’s 
apparent motion. Diameter not a line.” He found it on oyster and other shells and on 
alow. It is readily distinguished from S. spirorbis by the longitudinal ridges, and by the 
contrary turn of the volutions Under slate-stones at Kingsbridge Bay in great abundance 
(covering the surface) between tide-marks. He thought the sub-saline quality of the water 
so far up this inlet, at ebb tides, not congenial to other forms. Montagu,’ again, found Sprr- 
orbis carmatus common on Arca pilosa and Pinna ingeus on the south coast, and described 
it as having “a dull, opaque, white, spiral shell; the outer whorl rising into a carinated 
ridge on the top; the middle concave, sometimes pervious; the interior volutions incon- 
spicuous ; base a little spreading; aperture round. Size about half that of S. spororbis, 
from which it is readily distinguished by the angulated shape of the exterior whorl, which 
is formed like S. trequetra, but always regularly spiral.” Fleming® observes that the shell 
has two whorls, a narrow base and nearly vertical sides. Upper surface almost flat or slightly 
concave, with a central cavity surrounded by a sharp, rather elevated margin. The outer 
margin is nearly rectangular with a sharp edge. Outer surface is transversely wrinkled, 
the whole less regular than the preceding (S. granulatus), with the aperture more ascending.” 
_ His examples appear to have come from Shetland. Mérch, again, states that the tube is 
regularly spiral, with the outer whorl rising into a carinated ridge on the top. It is about 
half the size of S. spirorbis, and a little spreading at the base. Miss Bush* thinks Fleming’s 
form approaches S. quadrangularis, Stimpson, adding——“‘ but it is not improbable both species 
occur on the Hnelish coast.” She alludes to two forms, one dextral from Guernsey and 
Ireland, the other sinistral from Hneland, but comes to no definite conclusion. 
The tubes of S. carinatus (Plate CX XXIII, fig. 6) from Exmouth (W. Cocks, 1822) are 
small and have a reversed coil to that of S. heterostrophus, Mont. The inner side of the 
last whorl is broadly grooved, whilst a ridge runs along the top of the coil. The aperture is 
round, and the centre of the coil is either filled up by the early whorls or is blank—forming 
a large umbilicus. It resembles a young S. granulatus, but only one groove is distinct ; 
whereas Levinsen shows two ridges in his figure. The collar-bristles present numerous 
small serrations, only the upper being larger, on the rather long triangular base, followed 
by a gap and then the finely serrated tapering blade. The whole, therefore, approaches 
the bristle of S. granulatus. 
In the British Museum® another example of the second form, labelled S. carinatus, Mont., 
comes from Greenland, attached to a Polyzoon like a large Salicornaria, and forwarded 
1 “Test. Brit.,’ vol. ii, p. 503. 
? “Test. Brit.,’ vol. ii, p. 502, 18038. 
> ¢Wdin. Philos. Journ., vol. xu, p. 244. 
* <lubicolous Annelids from the Pacific,’ p. 249. 
> Tam indebted to Sir Sidney Harmer, Mr. Tate Regan and Dr. Calman for their courteous aid 
in the examination of this and other specimens in the collection. 
223 
