PYRAMIDULA ROTUNDATA. ISI 
Diagnosis.—P. rvtundutu is sufficiently distinguished from any other 
British species by the strong transverse sculpture of the whorls and their 
reddish flammular blotches. From its fossil ally Pyramidula ruderatu 
it is differentiated by its more depressed form; more numerous, more 
slowly increasing and more angulated whorls ; the reddish fleckings, and 
smaller mouth. 
Description.— ANIMAL comparatively small, slaty-grey in colour, darker on the 
back and paler towards the foot, and finely sprinkled with black at the sides ; 
TUBERCLES rather large and flat; MANTLE reddish-grey, marked with very close 
and distinet milk-white dots ; TENTACLES dark grey ; OMMATOPHORES closely 
approximating with stout bulbous extremities ; FOOT rather narrow. 
SHELL almost discoidal, but more depressed above than below ; WHORLS six or 
seven, slowly and regularly increasing, subcylindrical in shape, but with a sub- 
angulate periphery ; of a yellowish-brown colour, moderately opaque and glossy, 
and ornamented with a regularly placed series of rufous flames or blotches, which 
often alternate with those of the preceding whorl; the sculpture consists of curved 
transverse ribs, of which there may be 120 or more on the last whorl, with finer 
intermediate strive, which encircle the whorls and are only slightly stronger on the 
upper side; SUTURE well marked ; MOUTH transversely ovaliform, with a sharp 
and thin peristome, which is reflected basally and slightly infleeted above ; 
UMBILICUS extremely wide, open, and deep, exposing all the internal spire ; 
EPIPHRAGM very thin, whitish, and semitransparent. 
Diam. 7 mill. ; alt. 3 mill. 
INTERNALLY, the HEART lies well within the penultimate whorl adjacent to the 
aperture ; it is comparatively small and contracts rapidly. 
The NERVOUS SYSTEM has the component GANGLIA of the NERVE-RING noticeably 
more open and distinct, and the connectives and commissures longer than is usual 
amonest the true Helices, this open character allowing the buccal mass at will, to 
be protruded beyond or withdrawn within the NERVE RING; the CEPHALIC GANGLIA 
Fic. 234. Fic. 239. Fic. 236. 
Nervous, muscular, and cireulatory organization of Pyramidula rotundata, 
highly magnified. 
Fic. 234.—Brain-ring, with otocysts, of Pyramidula rotundata, x 25, 
c.g. cephalic ganglia; ~.g. pedal ganglia, showing otocysts ; a.g. combined abdominal and right 
visceral ganglia. 
Fic. 235.—Cephalic and pedal retractors of Pyramidula rotundata, X 10. 
om. ommatophore retractors; ¢.¢. lower tentacular retractors; / subsidiary foot retractors ; 
p. pharyngeal retractor. 
Fic. 236.—Renal organ or kidney and heart of Pyramidula votundata, X 10, showing also the 
looping of the intestinal canal by the cephalic branch of the aorta. 
k. kidney ; a. auricle ; v. ventricle. 
are large and distinct, joined by a long commissure; the PEDAL GANGLIA show 
the dull-white otoeysts which are large for the size of the animal on the middle 
of their posterior faces ; the VISCERAL GANGLIA show the usual constituents, those 
on the right side being largest, and the right pallial ganglion is fused with the 
abdominal ganglion. 
The CEPHALIC RETRACTOR becomes trifid at about one-third of its length, the 
MEDIAN MUSCLE being aftixed to the BUCCAL BULB and not dividing at the point of 
fixation; the paired TENTACULAR RETRACTORS each give off early a powerful slip 
to the FooT, and dividing again later to send a slender muscle to the lower tentacles. 
