50 REPORT OF NEW JERSEY STATE MUSEUM. 



also seen at times swimming about the Beverly wharf. Other 

 examples examined were taken at Atlantic City and Beesley's' 

 Point. Prof. Dahlgren reports it from Princeton. 



Petromyzon marinus Abbott, Geol. N. ]., 1868, p. 830. — 

 Abbott, Nat. Rambles, 1885, p. 479. 



Petromyzon americanus Le Sueur, Tr. Am. Philos. Soc. Phila., 

 I, 1818, p. 383.— Abbott, Geol. N. J., 1868, p. 830.— Abbott, 

 Rep. U. S. F. Com., 1875-76, p. 827. 



Petromyzon nigricans Abbott, Geol. N. J., 1868, p. 830. — 

 Abbott, Amer. Nat., 1870, p. 719. 



Ichthyomyzon appendix Abbott, Geol. N. J., 1868, p, 830. 



Class PISCES. 



The Fishes. 



Cold-blooded aquatic vertebrates which breathe by means of 

 gills not purse-shaped, but attached to cartilaginous or bony 

 gill-arches. Skull with lower jaw. Limbs developed as fins, 

 rarely wanting. Body usually covered with scales, bony plates or 

 horny appendages, sometimes naked. Median line of body with 

 one or more fins composed of cartilaginous rays joined by 

 membrane. 



Key to the sub-classes. 



a. Gill-opening 5 to 7 slits on each side of pharynx. elasmobranchii 



aa. Gill-opening single on each side. actinopteri 



Sub-Class ELASMOBRANCHII. 



Shark Like Fishes. 



Membrane bones of head undeveloped, except sometimes rudi- 

 mentary opercle. Skeleton cartilaginous. Skull without sutures. 

 No air-vessel. Intestine with 'a spiral valve. Arterial bulb with 

 3 series of valves. Optic nerves united by a chiasma. Cerebral 

 hemispheres united. Gills not free, attached to skin by outer 



