THE GASTROPODA 163. 
characteristically prosobranchiate. In Carinaria the shell is uncoiled 
and rudimentary, and there is no operculum. Pterotrachea has neither 
shell nor tentacles and is opisthobranchiate. Finally, Firoloida has lost 
the ctenidium. 
Faminy 1. ATLANTIDAE, Rang. Visceral sac and shell spirally coiled 
in one plane ; foot divided transversely into two parts, the posterior part 
bearing an operculum with a sinistral coil (Fig. 48), while the anterior 
part forms a fin provided with a sucker. Genera—Orygyrus, Benson ; 
shell capable of containing the entire animal, carinated only on the last 
whorl and near the aperture. Atlanta, Lesueur; shell capable of con- 
taining the whole animal, carinated throughout ; aperture with fissures 
(Fig. 141). Faminy 2. CartNarripag, Grasset. Visceral sac and shell 
conical and small in proportion to the rest of the body, which cannot be 
withdrawn into the shell ; foot elongated, fin-shaped, with a sucker but 
without an operculum. Genera—Carinaria, Lamarck (Fig. 142). Cardio- 
ae 7 ee i J 
eC —— 
—— 
Fig. 148. 
Pterotrachea mutica, seen from the right side. a, pouch for the reception of the snout when 
retracted ; br, ctenidiuin; c, pericardium ; g, cerebral ganglion ; g’, pedal ganglion ; i, intestine ; 
mt, posterior part of the foot ; n, so-called visceral nucleus ; oc, cephalic eye ; ph, pharynx; pr, 
fin-like anterior part of the foot ; v, oesophagus ; w, osphradium ; z, caudal appendage. (From 
Lankester, after Keferstein.) 
poda, @Orbigny (Fig. 142, C, D). Faminy 3. PreRorTRACHEIDAE, Gray. 
Visceral sac very much reduced, without shell and mantle ; anus on the 
posterior part of the body ; foot provided with a sucker in the male 
only. Genera—Pterotrachea, Forskal ; no tentacles ; actenidium present ; 
a filiform appendage at the posterior extremity of the foot (Fig. 143). 
Firoloida, Lesueur ; tentacles present, but no ctenidium and no posterior 
appendage to the foot. Pterosoma, Lesson. 
Sus-ORDER 2. STENOGLOSSA. 
Pectinibranchs in which the nervous system is much concentrated 
and always zygoneurous. The perioesophageal nerve-collar is always 
posterior to and is not traversed by the salivary glands. The stomato- 
gastric ganglia are situated close to the cerebral nerve-centres and far 
behind the buccal mass, the last-named organ being greatly reduced. A 
well-developed proboscis, an unpaired oesophageal gland (the gland of 
Leiblein or poison-gland), a pallial siphon, and a penis are always present. 
The osphradium is bipectinate, The radula is narrow, and in the 
majority of genera (Rachiglossa) has a single lateral on each side of the 
median or rachidian tooth: in the remainder of the group (Toxiglossa) 
there is no median tooth, and the radular formula is therefore 1.0.1. 
The sub-order is accordingly divided into two tribes. 
