756 FISHES — PETROMYZONTID^. 



Analysis of Genera or Petromyzontid^. 



'Maxillary teeth coalescent, forming a orescent shaped plate, with a distinct onsp at 

 each end, between which is sometimes a small median ca^p ; dorsal fin continuous. 



Ammocoetbs. 1. 



**Maxillary teeth double or triple, composed of two or three pointed cusps close 

 together, and not forming a crescent-shaped plate ; dorsal fin continuous. 



SCOLECOSOMA. 2. 



Genus 1. AMMOCffiTES. Dumeril. 



AmmocmUa, Dumeril, Faune Frangaise, 1828, (based on larval forms.) 

 Ichtkyomyzon, Girard, U. S. Pao. R. R. Surv., 1858. 



Type, Aminoomtes iranehialis, L., the larval form of Petromyzon planeri, Bloch, an 

 European species closely related to A. niger. 



Etymology, ammos, sand ; Icoite, to lie. 



Small Lampreys with the dorsal fin continuous, sometimes emarginate, but not 

 divided into fins, the posterior portion continuous with the anal around the tail, and 

 with the maxillary tooth single, forming a broad crescentic plate, with a large bluntish 

 cusp at each end, and sometimes a small cusp between them. But one American species 

 is known, very closely allied to the European Pride or Small Lamprey. 



1. Ammoccetes nigee (Rafinesque) Jordan. 



Small Black X^amprey. 



Petromyzon nigrum, Ramnesque (1820), Ichthyologia Ohiensis, 84. 

 Petromyzon niger, Joedant (1878), Man, Vert., first edition, 315. 



Amrnocmtes niger, Jokdon (1878), Man. Vert., second edition, 349. — JoRDON (1878), Bnll. 

 Ills. Lab. Nat. Hist., 2, 70. 



Deseription. — Head moderate, nearly as long as the chest (i. e. space occupied by the 

 gill openings) ; mouth comparatively small ; lips with a, conspicuous fringe of papillss ; 

 dorsal fin high, considerably depressed in front of the vent, but not divided into fins, 

 the pceterior part highest ; anal fin evident ; anal tube conspicuously protruded in the 

 spring ; eyes moderate ; maxillary tooth with its cusps large, triangular, well separated, 

 a small pointed median cusp usually present in the adult ; in younger specimens the 

 median cusp is obsolete, and in half grown individuals the tooth forms » curved plate, 

 without distinct cusps ; mandibulary plate curved with eight to ten well dev^oped sub- 

 equaUtooth-like lobes, inside of which is a plate bearing three teeth; a plate on each 

 side of the opening of the cesophagua, the remaining teeth inconspicuous. Bluish-black 

 above, silvery below ; size smail. Length, 6 to 10 inches. 



Habitat, Ohio Valley, Upper Mississippi, and Great Lake regiou. 



Diagnostic marks. — This speciee may bo known to be a Lamprey by its 

 sucking mouth and numerous gill openings. F»om the other Ohio 

 Lamprey, the form of the maxfllary tooth will distinguish it at sight. 

 The larvaj of the two without eyes or te«th are very similar, but the 

 present species is smaller and darker than Sc$lec6soma argent^m. 



