University of Michigan 



c^. Buccal funnel when expanded much greater in diameter 

 than the width of the body; supraoral lamina greatly con- 

 stricted, wnth one to four (usually two) approximated 

 cusps; anterior lingual lamina with anterior and posterior 

 transverse elements each provided with sharp denticles; 

 all disc teeth sharp and large; oral fimbriae arranged in 

 a double row; a high marginal membrane inside with 

 weakly ciliate border; intestine well developed and func- 

 tional in adults; larvae probably transforming at a size 

 of less than 120 mm. Basins of Hudson Bay, Great Lakes, 

 and Mississippi River. 



Ichthyomyson (Ichthyomyzon) concolor. 



C-. Buccal funnel constricted, when fully expanded not greater 

 in diameter than the width of the body; supraoral lamina 

 with two small, blunt, well-separated cusps ; anterior lin- 

 gual lamina with a single transverse element with minute 

 rounded denticles; all disc teeth weak and blunt, mostly 

 obsolescent; oral fimbriae presenting a matted appearance; 

 intestine degenerate and non-functional in adults ; larvae 

 transforming at a size of more than 120 mm. Great Lakes 

 basin. Ichthyomyson (Reighardina)- unicolor. 



Two distinct, more or less widely separated dorsal fins; dorsal 

 fin separated from the caudal by a sharp notch; caudal a 

 rather angular lobe; innermost lateral disc teeth enlarged, one 

 or more multicuspid. 



Genus Petromyzon 



d^. Anterior lingual lamina so sharply curved as to appear 

 as two sharply denticulated ridges, without a differentiated 

 median cusp ; supraoral lamina expanded behind the two 

 heavy divergent anterolateral cusps, which rarely are 

 imperfectly separated; infraoral lamina with 7 to 9 strong 

 cusps ; all teeth well developed and pointed ; four inner- 

 most laterals always bicuspid; buccal funnel wide; oral 

 fimbriae appearing to be arranged in several series, each 

 lateral and posterior fimbria being cleft two or three times 

 nearly to the base, each of the two or three lobes thus 

 formed again cleft and each of the minor lobes minutely 

 cleft; membrane forming edge of oral disc high, with 

 sharply ciliate border and with numerous well-developed 

 papillae along the inner base; myotomes between the last 



^Reighardina Creaser and Hubbs, new subgenus; orthotype, Ich- 

 thyomyzon fossor Reighard and Cummins (= Ichthyomyzon unicO'lor}. 



