406 SPIRORBIS GRANULATUS. 
sandstone the aperture is in a line with the tube, but where the tube is covered by Lepraliz, 
compound ascidians and other growths, or hampered by other tubes, the rounded aperture 
is curved upward, and thus is out of line with the tube. One character is the great size 
of the last whorl, which rapidly increases from the small original coil. Usually a dimple 
occurs in the centre. Some of the tubes are irregularly coiled, and in many a tendency to 
form a terminal process at the end of each ridge is evident. When the tube is dissolved by 
HCl a transparent, hyaline membrane is left, the larger outer coils presenting neither 
wrinkle nor transverse fold, whilst the early coils in the centre have so many that they 
resemble rouleaux of transparent discs. When lying in a coil of the tube of Pomatocerus the 
aperture is directed slightly upward. 
In a young example from St. Andrews, about one-third grown, the tube was perfectly 
smooth, rounded, and less closely coiled than usual. Such is probably a variety or abnormality 
and may have some relation to Montagw’s S. corrugata.' The eight branchize may belong to a 
young form. Yet Caullery and Mesnil (after Langerhans) describe it as distinct, with the 
first bristles devoid of a gap. In a rather small example from a stone in a tidal pool at St. 
Andrews in which only a single groove occurred on the tube, the structure of the bristles 
corresponded with that of the many examples of Sp. granulatus around it. It would thus 
seem that the single groove may occur as a variety. In a larger form only one groove and 
one ridge were distinct, but faint traces of the other occurred on minute examination. 
Besides the adults, numerous minute young with smoother shells occur onthe stones. Various 
irregularities of the tubes are common, irrespective of those crowded together. Swarms of 
the young of this species occasionally cover a limpet as specks just visible to the unaided eye. 
This form agrees with Montagu’s description (1803), having an opaque-white shell, of 
two volutions, deeply grooved longitudinally, and with a round aperture. He distinguished 
it from his S. heterostrophus by the whorls not being reversed, and by the deeper sulci. It 
is not clear what he means by the inner volution being nearly obsolete, only marked by the 
third or interior ridge. ‘‘This is white like glass-enamel, but not so glossy ; whereas S. 
heterostvophus is dull brownish or dirty white, and never grows to half the size.” He found 
it on rocks, on the under surface of loose stones at Milton, and on old shells, also at Guernsey 
on Haliotis “in company with a species of Serpula very different from any example of 
the genus hitherto described.’” ‘It has one very thick, rounded, glossy, white volution, 
very convex and wrinkled transversely, with a minute umbilicus at the top, and sometimes 
only a suture.”° 
It is possible that the Cornu Hammonis littoris of Plancus,* Tab. i, fig. 8, M. and N., 
Spirorbis, or Vermiculus saxis et lignis adherens refers to S. granulatus, the most common 
form on rocks and stones. 
Martini (1779) figures a Spirorbis with a grooved tube, the examples being clustered 
_ together on a rock-surface or other area, and closely resembling S. granulatus, though the 
locality is not stated. 
Turton’s Spirorbis granulatus, var. A. fasciata, a shell with two brown bands on the top 
1 «Montagu, ‘Test. Brit.,’ 11, p. 502. 
* He may refer to Spirorbis Caulleryt. 
3 “Test. Brit., 11, pp. 501—502. 
4 Janus Plancus Ariminensis, ‘ De Conchis, Venitis, 1739. 
