104 PROCEEDINGS OF THE MALACOLOOICAL SOCIETY. 



be said to pass into the frontal veil, and the area surrounding the 

 mouth is continuous with the sole. Dr. Willey and others who have 

 examined the specimen agree in thinking that this conformation, though 

 it may be teratological, is not due to distortion by alcohol. It is 

 remarkable, however, that the anterior region is not symmetrical : the 

 mouth is not in the median line of the foot, but to the left (looking 

 at the animal ventrally), and the oesophagus and buccal mass are not 

 directly behind the mouth, but to the left of it. 



The buccal mass is large, and provided with strong jaws, somewhat 

 similar to those of Tritonia Hbmbergi, but shorter and broader. The 

 radula is similar to that of Tritonia, but with fewer teeth in the low 

 than usual. The central tooth is like a truncated pyramid, the 

 anterior margin having a slight cleft, the continuation of which forms 

 a groove on the anterior side of the pyramid. The laterals are narrower, 

 irregularly triangular, and each provided with a long process. 



The liver is entire, and presents no diverticula, though it is divided 

 by a hollow in which lie part of the intestine and the stomach. The 

 nervous system, though not well preserved, appears to resemble that 

 of Tritonia, but no trace of eyes was discernible. The reproductive 

 system appears to be diaulic, and I could only discover one spermatheca. 



It appears, therefore, that this specimen is an aberrant member of 

 the Tritonia group, differing from others in the absence of branchiae, 

 of projecting rhinophore sheaths, and of all appendages, in the rounded 

 shape of the head, and in the ventral position of the mouth. These 

 remarkable characters are probably correlated with a burrowing habit. 



Bergh, in Semper's " Reisen im Archipel der Philippinen," Thl. ir, 

 Ed. ii, p. 726, and in his tract on the Nudibranchiate Grasteropods of 

 the North Pacific (Dall's "Scientific Results of the Exploration of 

 Alaska," vol. i, 1879, p. 154, figs.), has described an animal dredged 

 by Dr. Dall in 1872 at TJnalashka, which he identifies with Tritonia 

 tetraquetra, Pallas. Dr. Dall stated that the living animal had no 

 gills, and none appear in the drawing bv Pallas (in Nova Acta Acad. 

 Sci. Petrop., torn, ii, 1788, pp. 237-239, pi. v, fig. 22). Bergh 

 considers that it can hardly be true that the living animal possessed no 

 gills or appendages, 1 but the present specimen seems to show that 

 a large Nudibrauch without gills is found in the North Pacific. Both 

 the jaws and radula of our specimen correspond with those of Tritonia 

 tetraquetra, but the ventral position of the mouth and the rounded 

 shape of the head make it impossible to identify it with either Pallas's 

 figure, or with Bergh's description of the animal obtained by Dr. Dall, 

 which had also plumes around the rhinophores. 



In a recently published paper (" Danish Ingolf Expedition,'' vol. ii, 

 pt. 3, 1990, Nudibranchiate Gasteropoda), Bergh has described 

 a remarkable new form, which he names Doridoxa Ingolfiana, and 



It is not easy to reconcile the different statements respecting this animal, of which 

 there was apparently only one specimen, for though Dr. Dall said it had no gills 

 or appendages in life, and though in Semper's " Reisen" Bergh seems to say 

 that they must have been rubbed off, yet in pi. iii, fig. 14, of the Audibr. Moll, 

 of the N. Pacific, the latter author gives a drawing of a gill. 



