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 marimus Abbott, Geol. N. J., 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. ELAS MOBRANCHII 
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 
