194 Mr. C. T. Regan— ^ Synopsis of the 



groove, and the vertical fins are confluent. Tlie branchial 

 pouches communicate directly with the oesophagus. 



Family Petromyzonidse. 



Characters included in the ordinal diagnosis. 



Coasts and rivers of temperate regions, most or all 

 spawning in fresh water. 



The specimens enumerated are those in the British Museum 

 collection. 



Synopsis of the Oenera. 



I. Two tricuspid supraoral laminae 1. Mordacia. 



II. A single supraoral lamina. 



A. Anterior lingual lamina bi- or tricuspid ; supraoral lamina broad, 



quadricuspid 2. Geotria. 



B. Anterior lingual lamina with two curved denticulated ridges 



separated by a median longitudinal groove ; supraoral lamina 

 narrow, bicuspid 3. Petromyzon. 



C. Anterior lingual lamina with a single transverse denticulated 



ridge. 



1. Supraoral lamina narrow. 



Supraoral lamina bi- or tricuspid ; dorsal fins united. 4. Ichthyomyzon. 

 Supraoral lamina unicuspid ; dorsal fins separate . . 5. Caspiomyzon. 



2. Supraoral lamina broad, bi- or tricuspid. 



a. Disc covered with numerous teeth, radially arranged. 



6. Eudontomyzon. 



b. Disc with a marginal series of small teeth, an anterior group 



of teeth, and 3 or 4 enlarged teeth on each side ; no radial 

 series of teeth. 

 Last pair of lateral teeth connected by a posterior 



series of teeth parallel to the marginal series . , 7. Entosphenus. 

 Posterior part of disc toothless, except for the 



marginal series 8. Lampetra. 



1. Mordacia. 



Caraqola, Gray, Chondropt. p. 143 (1851), or Proc. Zool. Soc. 1851, 



p. 239. 

 Mordacia, Gray, t. c. p. 144, and /. c. ; Giinth. Cat. Fish. viii. p. 607 



(1870). 



Disc covered with radially arranged teeth. Two well- 

 separated tricuspid supraoral laminse ; infraoral lamina with 

 9 unequal cusps. Anterior lingual lamina with a V-shaped 

 denticulated ridge, the apex of the V directed backwards, the 

 most anterior denticle on each side more or less enlarged. 

 Dorsal fins separate. 



Australia ; Chile. 



