S. HA ITA. 



23 



the name of teeth, but are the merely hardened horny pro- 

 jections of the skin. 

 (2) The number of the cusps of the mandibulary tooth-plate is 

 described in P.fluviatilis as being seven or about seven. In 

 the Japanese species, this tooth-plate has constantly six cusps 

 of which the cusp at each lateral extremity of the plate is 

 bifurcated. 



I propose, therefore, to regard the Japanese form as a distinct spe- 

 cies and to call it Lampetra i) japonica. 



This Lamprey does not occur in all the parts of the empire, but is 

 limited to certain localities (see below). 



There has not been published any description of the smaller Lam- 

 prey 2 ) ; it differs from the larger form just stated not only in size but 

 also in the following essential characters : — 



(a) The suctorial disk is protruded more than in the larger one ; 



(b) The tooth-cusps are less prominent and more obtuse than in the 

 larger form, and the series of the teeth outside the mandibulary tooth- 

 plate consists of a lesser number than in the larger form ; the cusps at 

 lateral extremities of the mandibulary tooth-plate are not bifurcated ; 



(c) The first dorsal fin is not separated by a space from the second 

 dorsal, but there is only a notch befween them ; the anal fin in the 

 female attains in the spawning season a considerable height ; this is 

 called by S. H. Gage the fin-like appendage ; 



(d) The labial tentacles are mostly palmate ; 



(e) The skin is dark brown and shows faint irregular spots. This 

 species is thus in the external characters very close to P. planeri (Bl.). 

 In addition to these, two species show a great similarity in the external 

 configurations of brain (see below). But (1) the smaller size and 

 (2) the smaller number of the mandibulary tooth-cusps are the constant 



1) For the reason brought out further on, I have adopted the generic name Lampetra 

 for this species. 



2) V. Martens only touches it in his " Die Reise nach Ostasien." 



