3. MOKDACIA. 507 



middle ; thejirst is about one-third of its ovm length distant from the 

 second, which unites with the caudal, the point of junction being 

 marked by a depression. A fold of skin becomes perceptible on the 

 under edge of the tail, a short way behind the anus, and gradually 

 expands into the lower caudal lobe towards the tip of the tail, 

 where its height, in conjunction with that of the upper lobe, equals 

 the greatest height of the sceofid dorsal. Back and sides bluish 

 grey with irregularly scattered yellowish patches. Belly yellowish 

 white." 



West coast of North America. 



Dr. Ayres does not appear to have understood Richardson's de- 

 scription of the dentition ; it agrees quite with that given by 

 himself. 



2. Ichthyomyzon astori. 



Petromyzon astori, Girard, U. S. Pac. R.R. Exped. Fish. p. 380. 



The maudibulary plate bears six nearly equal teeth. First 

 dorsal separated from the second by an interspace. Body immacu- 

 late. {Oir.) 



Astoria, Oregon. 



3. IchthyomyzoD castaneus. 



Girard, I. r.. p. .381. 



The raandibulary plate bears nine teeth. Eyes small and incon- 

 spicuous. Dorsal fins continuous. Body itomaculate. (Gir.) 

 Galena, Minnesota. 



4. Ichthyomyzon hirudp. 



Girard, I. c. p. 382. 



The mandibulary plate boars seven teeth. Eyes small and incon- 

 spicuous. Dorsal fins continuous. Body immaculate. {Gir.) 

 Fort Smith, Arkansas. 



3. MORDACIA. 



Caragola et Mordacia, Grai/. 



Dorsal fins two, the posterior continuous with the caudal. The 

 maxillary dentition consists of two triangular gi-oups, each with 

 three conical acute cusps ; two pairs of serrated lingual teeth. 



C!hile and Tasmania. 



] . Mordacia mordax. 



rdromyzon mordax, Richards. Voy. Ereh. H)- Terr. Fish. pi. -38 (denti- 

 tion nut correct). 



]\Ioi'dacia mordax, Gray, Chondropt. p. 144, tab. 1. fig. (cop. 

 liichard.-i.). 



Caragola lapicida, Gray, I. c. p. 14-3, tab. 1. fig-. 5, or Pruc. Z/>ol. 8or. 

 iHol.p. 2.39. 



