438 



PTEROPODA — GYMNOSOM ATA 



CHAP. 



conical, no lateral gill, posterior gill with three radiating crests, 

 skin pigmented. Notobranchaea is the single genus. 



Fam. 4. Clionidae. — Body long, angulated behind, proboscis 

 short, mouth with two or three pairs of appendages, no jaw, no 

 gills. 



Clione limacina is so abundant in Arctic seas as at times to 

 colour the surface for miles. Each of the cephalic appendages 

 has about 60,000 minute pedicellated suckers. 



Fig. 291. — a, An- 

 terior portion of 

 Pneumoderma; 



B, Clione lima- 

 cina Phipps ; 



C, Halopsyche 

 Gaudichaudi 

 Soul. ; /, /, fins ; 

 h.s, h.s, hook- 

 sacs; l.f, lobe of 

 the foot; s, s, 

 suckers; o, pos- 

 terior genital 

 orifice; t, t, 

 tentacles. (After 

 Souleyet.) 



Fam. 5. Halopsychidae. — Body ovate, thick, rounded behind, 

 no gill or proboscis, fins long, narrow, broadened at the ends, 

 epidermis sub-cartilaginoid. 



Halopsyche Q = Euryhia) has the power of withdrawing its 

 head completely into a sort of pocket, which is closed by an 

 anterior fold of the mantle. There are two long non-retractile 

 buccal appendages. 



Order IV. Pulmonata 



Gasteropoda with two pairs of tentacles, visceral loop euthy- 

 neurous, ganglia concentrated round the oesophagus ; breathing 

 air by a pallial cavity formed by the union of the front edge of 

 the mantle with the cervical region, sexes united, shell present 

 or absent, no operculum^ (except in Amphihola). 



Sub-order I. Basommatopliora. — Eyes generally at the 

 base of the tentacles, which are not retractile, male and female 

 genital orifices separate, radula (p. 235) multiseriate, shell 

 always present, external. Fresh water or quasi-marine. 



1 An operculum is said to exist in the young forms of Auricula and Parmacella. 



