The Lake and Brook Lampreys of Neiv York 437 



that of the lake and of the marine lamprey. This difference 

 in dentition, and perhaps also some other considerations, have 

 led some zoologists to divide the genus Petromyzon into two, 

 Petromyzon and Ammocoetes, and in this case the brook lam- 

 prey is placed in the latter genus.* 



In .size the brook lamprey varies from 140 to 200 millimeters. 

 The color is nearly uniformly dark in the dorsal half and 

 gradually changes almost to white on the ventral surface. 

 The two dorsal fins are said to be continuous with only a 

 sharp notch between them. As the description of this form 

 in America has been based entirely on specimens taken at the 

 spawning season (Jordan, '85, p. 294), the two dorsals could 

 not be described otherwise than as continuous. But, as with 

 the male lake lamprey, this is a feature of the spawning sea- 

 son. In just transformed ones taken in October, there is a 

 considerable interval between the two dorsals, with only an 

 exceedingly low ridge connecting them, a ridge which in the 

 fresh specimen is very difficult to make out. The figure given 

 is of a preserved specimen (PI. IV, fig. 13). 



The brook lamprey of North America is believed by Jordan 

 to be the same species as the brook lamprey of Europe ('85, 



* It seems unfortunate to the writer that, if the genus Petromyzon 

 must be divided, some other name could not have been found for the 

 brook lamprey. When larval lampreys were not known to be the tad- 

 pole stage, so to speak of the lampreys, but supposed to be entirely dif- 

 ferent forms, they were put into an independent genus and called Am- 

 mocoetes. Upon the discovery, by A. Miiller ('56), that the animals pre- 

 viously placed in the genus Ammocoetes, were merely a larval stage of 

 a lamprey he made the following suggestion, p. 332 : " Somit ist nach- 

 gewiesen, dass aus den Neunaugen die Querder eutstehen, und dass die 

 Querder zu Neunaugen warden. So sind denn auch die Querder, wo sie 

 sich im Systeme bliken lassen, wegen Fiihrung des falschen Namens 

 anzuhalten, und als Unmiindige ihren respectiven Eltern zu unterstellen. 

 Der Name Ammocoetes kann fortan nur die Larven der Neunaugen be- 

 zeichen, wie Gyrintis dC\^ der Frosche." Milne- Edwards supports this 

 suggestion and urges that the term be used for the larvae of the Petro- 

 nyzontidae as the term " tad-pole, gyrinus," is used for the frog's young 

 (Milne-Edwards, '57, tome 2, p. 246). This suggestion has been adopted 

 by nearly all morphologists, and the word is frequently used as an adjec- 

 tive, thus ammocoetes stage, ammocoetes form, etc. 



