PNEUMODERMATIDAE 289 



A living specimen of this species was found by the Siboga Expedition near Damar 

 Island, while conchae were taken at five stations lying between lat. z° 3' and 10° 35' S, 

 long. 117° 4' to 131° 26' E. 



PTEROTA (GYMNOSOMATA) 



The naked Molluscs which form this group among the Tectibranchs are not nearly 

 related to the Pteropoda, but are alHed to the Aplysioidea. Owing to their minute size 

 and to the frequently contracted state of their bodies they are not easy to study. Only 

 extended individuals of particular species measure more than an inch in length. The 

 average size is about that of a grain of wheat and many are much smaller. The buccal 

 appendages and gills vary in the difTerent families and in contracted specimens can only 

 be determined by dissection. There is no paUial cavity and no gizzard with plates. The 

 liver-pancreas adheres to the stomach, and the cerebral ganglia are attached to one 

 another instead of being united by a commissure. The radula has usually a number of 

 lateral teeth. All the group are carnivorous and feed principally on the Thecosomata. 

 Although a pair of fins would seem to be a necessity to their active life, abnormal 

 specimens of Piieumoderrnopsis paucidem (Boas) have been observed (Massy, 1917, 

 p. 231) in which only the right fin was developed in nearly all the specimens of a haul. 



Family PNEUMODERMATIDAE 



Genus Pneumoderma, Cuv., 1804 



Pneumoderma atlanticum (Oken), 18 16. 



Pneumodermopsis atlantica, Oken, 181 6. 



Pneumodermon Peronii, Lamk., 1819 {nee Boas, Pels., Meis., Tesch). 



Pneumoderma violaceum, d'Orb., 1840; Boas, 1886; Pels., 1888; Meis., 1898; Tesch, 1913. 



St. 276. Young-fish trawl, 150 (-0) m. : 2 specimens. 



Both these specimens were captured off the Congo river. 



They were retracted, and measured about 6-5 mm. in length. The suckers and 

 radula were examined. 



The family Pneumodermatidae possesses a dorsal glandular patch; a lateral gill; 

 sucker-bearing arms; a median jaw and hook sacs. 



The genus Pneumoderma has two sucker-bearing arms, a posterior gill, long hook sacs, 

 radula n-o-n in the adult, n-\-7i in the young. The present species has a radula of 4-0-4 

 and the suckers on the arms are numerous ; the largest are near the mouth and they be- 

 come smaller distally. Mme Pruvot-Fol (1924, pi. xv, fig. i) gives a fine illustration of a 

 fully extended specimen with about 33-40 suckers on each arm. The synonymy of this, 

 the oldest described species of the genus, is fully explained in the same paper. 



Distribution. Atlantic, Pacific, Mediterranean. 



