8 University of Michigan 



12. Cusps of supraoral usually bitubercular, always weak and 

 rounded, separated by a short, narrow isthmus, the base 

 of the cusps poorly developed; infraoral lamina without 

 distinct denticles, the crest crenulated or even nearly 

 entire; all teeth greatly reduced; the anterior field of the 

 disc with but few (about four) denticles, placed laterally 

 and separated by a broad toothless median area ; the three 

 laterals of each side obsolescent, with scarcely developed 

 bases, sometimes unicuspid or with the two or three cusps 

 isolated as more or less widely separated denticles ; myo- 

 tomes fewer, 54 to 60 between the last gill opening and 

 vent. Ohio and Potomac River basins. 



Lampetra (Okkelbergia)^ lamotfcnii. 



Notes ox the North American Species 

 I. Ichthyomyzon concolor Kirtland 



Ammocoeites concolor Kirtland appears to have been based 

 on the larva of the present species. It is certainly a species 

 of Ichthyomyzon, and "the irregular series of dark brown dots" 

 mentioned by Kirtland are not developed in the other species 

 of the genus. Furthermore, /. unicolor is not known to occur 

 in the Ohio drainage, where the type of concolor was obtained. 



Forbes and Richardson^ have demonstrated the specific iden- 

 tity of Ichthyomyzon castanens with /. concolor. In our own 

 study we have found abundant confirmation of this view. 



2. Ichthyomyzon unicolor DeKay 



The degenerate relative of Ichthyomyzon concolor, lately 



described by Reighard and Cummins,^" is so distinct that we 



regard it as the type of a new subgenus, Reighardina (defined 



on p. 4). It has subsequently been referred to as "Ichthy- 



8 Okkelbergia Creaser and Hubbs, new subgenus ; orthotype, Ammo- 

 coetes aepyptera Abbott {^Lampetra lamottenii) . 



9 The Fishes of Illinois, Nat. Hist. Surv. 111., Vol. 3, 1908 (Ed. 2, 

 1920), p. 10. 



lOQcc. Pap. Mus. Zool., Univ. Mich., No. 31, 1916, pp. 1-12, pis. 1,2. 



