3. MORDACIA. 507 



middle; thejirst is ahout one-third of its own length distant from tlie 

 second, which unites with the caudul, the iwiut of junction being 

 marked by a depression. A fohl 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 second dorsal. liack 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. 

 Peti'omyzon astori, Girard, U, S. Pac. R.R. Exped. Fish. p. 380. 

 The mandibulary plate bears six nearly equal teeth. First 

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

 late. {Oir.) 



Astoria, Oregon. 



3. Ichthyomyzon castaneus. 

 Girard, I. c. p. 381. 

 The mandibulary plate bears nine teeth. Ej-es small and incon- 

 spicuous. Dorsal tins continuous. Body immaculate. (Oir.) 

 Galena, Minnesota. 



4. Ichthyomyzon hirudo. 



Girard, I. c. p. 382. 

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

 sincuous. Dorsal fins continuous. Body immaculate. (Gir.) 

 Fort Smith, Arkansas. 



3. MORDACIA. 



Caragola et Mordacia, Grai/. 



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

 maxillary dentition consists of two triangular grou])s. each with 

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



Chile and Tasmania. 



1 . Mordacia mordax. 



Pctroinyzon mordax, Jlichards. Vo\j. Erch. is- Terr. Fish. pi. 38 (denti- 

 tion not correct). 



Mordacia niQi-dax, Gray, Chmdropt. p. 144, lab. 1. fig. 6 (cop. 

 Jiicltards.). 



Carai'ola lapicida, Graf/, I. c. p. 143, tab. 1. fig. o, nr Proc. Zool. Sue. 

 lS?)l,p. 239. 



