ATLANT. DEEP-SEA EXPED. 1910. VOL. III]. 



PTEROPODA. 



57 



Fig. 44. Radula of Pneumoderma atlantica. 



A 



B 



Fig. 45. Buccal organs of Pneumoderma atlantica: r. radula; 

 j. jaw; h. hook-sacs; B. One of the hooks. 



described by Tesch (1904) is his new species Clionopsis 

 microcephalus, which has a genital gland outside the 

 body near its posterior end. A difference between the 

 two species is seen in the want of a cover round the 

 gland in Clionopsis, while in our species the gland is 

 surrounded by a closed spherical sac. 



It is of interest to note that the two species, in which 

 this strange arrangement has been observed, belong to 

 different families of gymnosomatous pteropods. 



To complete our description of the species: — 



Radula: formula 4—0—4; lateral teeth hook-shaped, 

 those of the second longitudinal row being the largest 

 (textfig. 44). 



Jaw: A short cylindrical papilla composed of two 

 symmetrical halves carrying 6 small spines along each 

 side of its distal end (textfig. 45 j, and fig. 52, pi. VI). 



Hook-sacs tube-shaped, about three times the 

 diameter in length. The hooks are largest on the median 

 side of the evaginated sac, where they are arranged in 

 two longitudinal rows, while smaller hooks are scattered 

 over the whole surface (fig. 51, pi. VI). 



Acetabuliferous appendages: two symme- 

 trically developed arms fixed to the proboscis, each carrying 

 numerous (about 50) small suckers. 



Foot with broad quadrangular lateral lobes, and a 

 short posterior lobe broad at the base and narrow at 

 the point. 



Gills: lateral gill a small simple protrusion on the 

 right side of the body: posterior gill not observed. 



Pneumoderma atlantica is distinguished from other 

 species of the genus, inter alia by the acetabuliferous 

 appendages being fixed to the proboscis. 



Locality: Station 62 (36° 52' N, 39° 55' W). 

 Surface. 



Pneumoderma sp. 



Radula: Formula 4—0—4. Two or three rudiments 

 of median teeth (of the family type) are found in the 

 youngest part of the radula (textfig. 46); lateral teeth on 

 broad basal plates, those of the second longitudinal row 

 largest. 



Jaw unknown. 



Hook-sacs tube-shaped, with hooks like those of 

 P. atlantica (textfig. 47 A— B). 



Acetabuliferous appendages present; shape 

 unknown. 



Foot: Lateral lobes thick and hollow like small 

 hemispheres; postertor lobe very short triangular (textfig. 

 48 B). 



Gills: Lateral gill a transverse fold of the skin on 

 the right side of the body, from which three longitudinal 

 ridges extend forwards; posterior gill unknown. 



The peculiar shape of the foot of this specimen might 

 perhaps form the basis of its diagnosis as a new species, 

 but the whole body is so strongly contracted that I think 

 it better at present to have this question undecided. 



Locality: Station 42 (28° 2' N., 14° 17' W.). 



Date: 23 / 6 - 2i / 5 . 



Depth: 250 metres. 



