22 



ON THE LAMPKEYS OF JAPAN AND SIBERIA. 



A. On the Species of the Japanese Lampreys. 



A collection of the Japanese Lampreys falls naturally into two 

 groups ; (1) a larger form measuring 39.0 — 50.7 cm in length and (2) a 

 smaller one having length of 8.0 — 15.6 cm. The larger form is undoubt- 

 edly the one described by v. Martens under the name of Petromyzon 

 japonicus. Unfortunately I have been unable to see the original descrip- 

 tion. Günther !) makes the following remark on it : " Petromyzon 

 japonicus, Martens, Wiegln. Arch. XXXIV, p. 3, does not appear to be 

 specially distinct from P. ßuviatilis. The dentition in both is extremely 

 similar, only the Japanese example has an additional transverse series of 

 small teeth hehind the mandi bulary tooth. The figure accompanying the 

 description of P. japoiiicus is incorrect and I am indebted to Pro- 

 fessor Peters for re-examination of the typical specimen " (p. 504) 



Prof. Jordan has called it, m his " Preliminary Check List of 

 the Fishes 2 ) of Japan, " Petromyron japonicus following Martens' 

 nomenclature. 



As Günther states, this form of the " Japanese Lamprey closely 

 resembles P. ßuviatilis, that is, the position of the fins, the coloration of 

 the body, the branching mode of the marginal tentacles of the suctorial 

 disk, the maxillary tooth, the lingual tooth, the teeth of the suctorial 

 disk, the structure of the brain (see below), &c. all agree with those de- 

 scribed in P. ßuviatilis. But there are found two points of constant 

 differences : — 



(1) The first point has already been noted by Günther. He 

 notes " an additional transverse series of small teeth behind 

 the mandibulary tooth." I would replace the word "behind" 

 with the word " inside," because this series of the teeth is 

 found immediately inside the mandibulary tooth-plate. It 

 should be noted that these teeth which are 3 — 4 in number 

 are, so far as I am aware, not yet enough hardened to deserve 



1) Günther. Cat. of Fishes, vol. VIII. 



2) This Journal, vol. Ill, pp. 31—159, 1891. 



