12 



Order X. HOLOCEPHALI. 



Endo-skeleton cartilaginous ; exo-skeleton as placoid granules ; most of the fins with a strong spine 

 for the first ray, ventrals abdominal ; gills laminated, attached by their margins ; a single external gill- 

 aperture ; no swim-bladder ; intestine with spiral valve. Copula gaudent. 



Fam. Chimeridte. Example, Chimaera. 



Edaphodontidee. 



LPassalodon. 



Order XI. PLAGIOSTOMI. 



Endo-skeleton cartilaginous or partially ossified ; exo-skeleton placoid ; gills fixed, with five or more 

 gill-apertures ; no swim-bladder ; scapular arch detached from the head ; ventrals abdominal ; intestine 

 with spiral valve. Copula gaudent. 



Fam. Hybodontidae. Example, Hybodus. 

 Sgualidce. Shark. 



Raiidce. Ray or Skate. 



Order I. DERMOPTERI. 



Suborder!. CIRROSTOML 



* 



(See Prep. No. 8, Branthiostoma, as an example of a skeleton of this Order of Fishes.; 



Suborder II. CYCLOSTOMI. 



34. The skull and part of the vertebral column, with the branchial and pericardial 

 cartilages of the Lamprey (Petromyzon marinus). No part of the skeleton in 

 this low organized fish is advanced^ histologically, beyond the cartilaginous 

 stage. 



In the skull the basi-occipital cartilage is continued backwards, in the form of two slender 

 processes, upon the under part of the notochord into the cervical region. The hypophysial 



