4 University of Michigan 



bilateral symmetry — a dilTerent number on tbe two sides, as in 

 the type. In several specimens extraorals are indistinguishable. 

 Disc teeth vary in size and number ; in specimens where they 

 are prominent four teeth may be made out within each radiat- 

 ing series over entire surface of disc. Where the dentition is less 

 strong three, two, or only one may constitute a series poste- 

 riori}- ; l)ut always with three in each series anteriorly and lat- 

 erally, in several specimens no di.sc teeth can be made out.- 

 It is needless to say that weak disc dentition is associated with 

 weak extraorals, su])raorals, etc. Infraoral lamina has <S to lo 

 cus])s, always more or less irregular, as in tlie t\pe. Tlie anal 

 tin in females ( PI. I, fig. 3 ) is higher and more convex in out- 

 line than in males. Females ])Ossess a fin-like swelling anterior 

 to vent. The urinogenital papilla in females does not ])rotrude 

 from the vent. Pronounced individual variation in propor- 

 tions of the Ijody occurs here, as in other lampreys. These 

 variations, as well as dififerences in the numl)cr of muscular 

 impressions, are presented in the following table : 



- The teeth are iinich more readily seen if siained yellow by immersiiitj the 

 oral disc for five minutes in a saturated solution of picric acid in '/o% alcohol. 

 The specimen may then be placed in 70% alcohol, in which the color is but slowly 

 extracted. 



