, 
134 ZONITOIDES EXCAVATUS. 
Diagnosis.—Resembles its congener, Z. nitidus, but differs in the 
greater convexity of the shell above and beneath, and especially by its 
very wide umbilicus ; the whorls are also more rounded and more closely 
coiled, and the last not so large in proportion to the rest; the strize 
also are rather stronger. 
INTERNALLY, it displays as a noticeable and distinctive feature the 
whiteness of the arterial system, due presumably to lime, as in Arion. 
The ramifications of the vessels, especially of the hepatic artery, are as 
distinct as in Arion ater, and the abrupt termination of the smaller 
branches is just as striking. 
Description. —ANIMAL with a slender BODY, very pale slate or whitish with a 
bluish-grey tinge towards the HEAD, very rarely black, with the usual dorsal 
furrows; TAIL narrow and keeled, and not reaching to the margin of the shell 
when crawling ; FOOT-SOLE trifasciate, the central area slightly darker than the 
pale bluish-grey side areas; MANTLE closely covered with white specklings ; 
TENTACLES somewhat long, only slightly bulbous at the extremity, the black 
ocular points showing up very distinctly on the white surroundings; when the 
tentacles are withdrawn the eye-specks are distinctly visible beneath the skin ; 
lower tentacles short; LOCOMOTORY MUCUS not very copious, thin, and slightly 
iridescent. 
INTERNALLY, the SUPRA-GSOPHAGEAL 
ganglia are large and white, the ecompon- 
ents are closely approximate but connected 
by commissures; the GANGLIA are as usual 
largest on the right side of the body ; the 
SUB-CESOPHAGEAL ganglia are greyish; 
the OTOCYSTS on the posterior face of the 
pedal ganglia showing up white against 
the grey mass ; the HEART is of a lenticular 
shape, constituted by a transparent pearly- 
white auricle and a pale-grey ventricle of Fig. 179. Se bec ORE eeatne ee ee 
nearly equal size and of similar pyriform andes Jccddites GRO TENO EIA on lower 
shape, joined together by a slender neck, face of pedal centres, x 10. 
Fic. 179. Fic. 180. 
the ventricle fitting into the auricle like Fic. 180.—Renal crgan or kidney and heart 
a ball into a socket, the whole enclosed of 2. excavatus, x 10. ‘ 
within a thin and transparent peri- doidney 702, aumbles\7/.venticle: 
eardium ; the KIDNEY is greenish-grey in colour with fine anastomosing lines. 
The ALIMENTARY SYSTEM is 
composed of a long and slender 
(ESOPHAGUS, upon which the SALI- 
VARY GLANDS rest; these are 
usually distinct, but sometimes 
blend together, and have long dark 
vrey ducts; the Crop is somewhat 
oval in shape, yellowish-brown in 
colour and imbedded in the diges- 
tive gland or liver, which is of a 
deep-brown, upon which the opaque- 
white branches of the hepatic artery 
are very conspicuous and striking. 
The MUSCULAR SYSTEM as dis- 
played by the BUCCAL RETRACTORS 
is much as in the typical Hyalinia Fic. 181. Fic. 182. 
cellaria; the PHARYNGEAL and 
Fic. 181.—Underside of Penultimate and Superior 
paired i ENTACULAR RETRACTORS whorls of Zonttoides excavatus, showing arrangement 
each arise from a distinct and of the organs, x 6. 
separate point of the ereat colum- ot. ovotestis ; Z. liver; 7. intestine ; &. kidney ; /. heart; 
oe. esophagus ; s.0. s ca yiduct. 
ellar muscle; the pharyngeal re- Meneses gait gr 
tractor, which is very broad’ and is Fic. 182.—Buccal retractors of Z. excavatus, X 10. 
only slightly cleft before its junction with the buccal bulb, tapers gradually to its 
origin on the upper surface of the columellar muscle ; the right and left tentacular 
retractors originate from the corresponding right and left margins of the colum- 
ellar muscle, giving off slender branches to the lower tentacles. — 
