50 Dr. E. von Martens on the Occurrence of 



dark or brownish-grey, densely studded with minute papillae; 

 speckled with black, angular or irregular maculae ; a yellow me- 

 sial line down the back ; margins edged with a yellowish or pale 

 band ; superior pair of horns hyaline, the buccal pair yellowish- 

 grey. 



The body never makes any approach to linear even when 

 most extended; it is always rather broad, and fully rounded 

 posteriorly, less so at the anterior extremity. There is no de- 

 fined margin separating the central part from the edges; the 

 latter are merely a little flatter : there is not the least trace of 

 solid material in the covering or in the substance of the body. 

 The superior pair of horns are cylindrical, somewhat longish, 

 and terminate in a little rounded bulb, on the upper surface of 

 which the minute black eye is imbedded ; the buccal pair is bi- 

 lobed, but not deeply sulcated, appearing exactly as if two short 

 cylinders were under a skin. The foot terminates a little before 

 the end of the mantle; it occupies in breadth about one-fifth or 

 rather more of the under surface, and is separated by a deep 

 groove from the mantle, so that it appears as if winged : it 

 has about 200 transverse rugae in the inch, which, in the ad- 

 vancing movement of the animal, present precisely the, same 

 appearance as the legs of Julus, a wave running from behind 

 forward, about six rugae forming each wave, with an interval of 

 fourteen to eighteen between them. The under surface of the 

 body of the animal on each side of the foot is covered with 

 minute papillae or tubercles, about 180 in an inch. 



The habits of the animal, as far as I had an opportunity of 

 examining them, appear to difi'er in no respect from those of 

 Limaon, 



EXPLANATION OF PLATE IL B. 



Fig. I. Vaginula maculata. 



Fig. 2. Ocular tentacle. 



Fig. 3. Section of buccal tentacle. 



Fig. 4. Transverse sections of body. 



Fig. 5. Lower surface of body and foot. 



Fig. 6. Vaginula ? 



VIII. — On the Occurrence of Marine Animal Forms in Fresh 

 Water, By Dr. E. von Martens*. 



The genera Sphceroma and Palcemon, Gohius and Blennius occur 

 plentifully in the North Sea, but are entirely unknown in the 



[* Translated by W. S. Dallas, F.L.S., from Wiegmann's Archiv, 1857, 

 p, 188, This paper forms the third section of a long memoir '* On some 



