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756 FISHES—-PETROMYZONTIDE. =. 
ANALYSIS OF GENERA OF PETROMYZONTIDZA, 
“Maxillary teeth coalescent, forming a crescent shaped plate, with a distinct cusp at 
each end, between which is sometimes a small median cusp; dorsal fin continuous. 
AMMOCGTES. 1, 
**Maxillary teeth double or triple, composed of two or three pointed cusps close 
together, and not forming a crescent-shaped plate ; dersal fin continuous. 
SCOLECOSOMA. 2. 
GENUS 1. AMMOC(THS. Dumeril. 
Anmocetes, DUMERIL, Faune Frane¢aise, 1828, (based on larval forms.) 
Ichthyomyzon, GIRARD, U.S. Pac. R. R. Surv., 1858. 
Type, Ammocates bitinchialis, L., the larval form of Petromyzon planeri, BLOCH, an 
European species closely related to A. niger. 
Etymology, ammos, sand; Katie, 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 betweenthem. But one American species 
is known, very closely allied to the Kuropean Pride or Smal! Lamprey. 
1. AMMOC@TES NIGER (Rafinesque) Jordan. 
Small Biack Lamprey. 
Petromyzon nigrum, RAFINESQUE (1820), ichthyologia Ohiensis, 84. 
Petromyzon niger, JORDAN (1878), Man. Vert., first edition, 315. 
Ammocates niger, JORDON (1878), Man. Vert., second edition, 349.—JoRDON (1878), Bull. 
Tils. Lab. Nat. Hist., 2, 70. 
Description.— Head moderate, nearly as long as the chest (i. e. space cecupied by the 
gill openings) ; mouth comparatively small; lips with a conspicuous fringe cf papille ; 
dorsal fin high, considerably depressed in front of the vent, but not divided into fins, 
the posterior part highest; anal fin evident; anal tube conspicuously protruded in the 
spring ; eyesmoderate; maxillary tooth with its cusps large, triangular, well separated, 
a small pointed median eusp usually pressnt in the adult; in younger specimens the 
median cusp is obsolete, and in half grown individuals the tooth forms a curved plate, 
without distinct cusps ; mandibulary plate curved with eight to ten well devéloped sub- 
equal,tooth-like lobes, inside of which is a plate bearing three teeth; a plate on each 
side of the opening of the esophagus, the remaining teeth inconspicuous. Bluish-black 
above, silvery below; size smadl. Length, 6 to 10 inches. 
Habitat, Ohio Valley, Upper Mississippi, and Great Lake region. 
Diagnostic marks.—This species may be known to be a Lamprey by its 
sucking mouth and numerous gill openings. From the other Ohio 
Lamprey, the forma of the maxillary tooth will distinguish it at sight. 
The larve of the two without eyes or teeth are very similar, but the 
present species is smaller and darker than Scolecosoma argenteum. 
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