NILS HJ. ODHNER, PTISANULA. LIMN^EOIDES. 5 



middle-part of the sole and to receive in its fundus the ef- 

 ferent duct of the foot-gland (Fig. 5). 1 The head is covered 

 with a large cephalic dise, somewhat sinuous in front but 

 without any trace of tentacles and without any median fur- 

 rovv. The disc is abruptly terminated behind. In the outer 

 and hind parts of the disc the superficial eyes are visible. 

 The colour of the animal is a darkish brown. 



The Inner Anatomy. From the shape of the shell, 

 the radula and the exteriör morphology of the animal no 

 definite conclusions as to the relations of the present form 

 can be drawn. The presence of a cephalic disc gives rise to 

 the supposition that it may belong to the group Cephalaspi- 

 dea of the Tectibranchiate Opistobranchia; the shell reminds 

 one more of Actoeon than of anything else, but the radula 

 and the absence of operculum as well as of parapodia at the 

 foot-margins indicate affinity to the genus Diaphana of the 

 family Scaphandridce. In order to prove the correctness of 

 this supposition, I have examined a specimen microscopically 

 from sections. From the result the fact can be stated that 

 no stomach-plates, which are much characteristic features of 

 many of the genera of Tectibranchia, are present. In this 

 respect too there is agreement with Diaphana. For compa- 

 rison, therefore, I cut a specimen of Diaphana hyalina from 

 Bohuslän and a specimen of its variety glacialis from Spitz- 

 bergen; these will also be dealt with and referred to in the 

 following account. 



The Intes tinal Can al. The mouth of Ptisanula has 

 no jaws, as is the case too with Diaphana. At the sides of 

 the labial disc a pair of buccal glands debouch in both forms, 

 just as in Actoeon, Hermcea and other Nudibranchs, The 

 pharyngeal cavity is furnished with a cylindrical epithelium 

 that in Diaphana has cilia on its surface and a thin cuticula 

 in Ptisanida. Further back in the expanded pharyngeal 

 bulbus the epithelium becomes a cuticula, which in Ptisanula 

 is remarkably thick. The walls of the bulbus are as usual 

 muscular. In front of the radular sheath a pair of salivary 

 glands debouch into the pharynx; these are very small in 

 Ptisanula, larger in Diaphana. The oesophagus starts from 

 the upper side of the pharynx, as usual; in Ptisanula it was 

 bent back upon itself into a coil, the first bend of which was 



1 Civ Neivnesia, E. A. Smith, 1902. 



