164 



TETRASTEMMA. 



course of the dorsal and ventral furrows is such that when the snout is seen in profile, a somewhat 

 acute angle is formed at their junction on the side. 



This is another interesting species supplied by the rich tangle-roots on the mussel-ground of 



Fig. 10. 



Fig. 11 



Outline of the anterior dorsal 

 region of Amphiporus bioculatus. 

 Enlarged. 



Ventral surface of the 

 anterior region of 

 A. hioculatus. 



Bressay Sound. It lives well in confinement, and it can be observed that, instead of the 

 usual gliding progression of its allies, this form moves its snout in a boring manner. 



The specimens were loaded with fully-developed spermatozoa in the beginning of August. 



Genus II. — Tetuastemma, 1 Bhrenberg, 1831. 



Like many others of the race, the species of this genus were included amongst the Fasciolte 

 by 0. F. Miiller, the first who, in the ' Zoologica Danica,' clearly described a species (Fasciola 

 Candida). Ehrenberg, in establishing his genus Tetrastemma, in 1831, seized upon a very 

 constant character; but we must dissociate it from many of the genera which formed along 

 with it the anomalous Family Gyratricina. Though he describes the proboscis as being exserted 

 from a transverse fold of the snout in his typical species, and hence apparently connecting it with 

 Keferstein's Prosorhochmus, an attentive examination of the other parts of his description and 

 his figures has convinced me that he alludes to a form identical with one not uncommon in 

 Britain, viz., Tetrastemma flavida. 



Generic character. — Eyes four ; arranged so as to indicate a square or oblong. 



1 Terpag, four, otejUjUci, a crown. 



