360 CRETACEOUS FISHES. 
Subking¢dom VERTEBRATA. 
Class PISCES. 
The remains of fishes occur in extraordinary preservation in the chalk forma- 
tion. No one who has seen Dr. Mantell’s superb collection, now in the British 
Museum, can ever forget the beautiful specimens which he collected in the vici- 
nity of Lewes; paleontologists are much indebted to him for his great perse- 
verance in developing and explaining the general characters of these magnificent 
fossils. 
M. Agassiz has divided the class Pisces into four Orders, according to the 
characters of the external covering, a most useful arrangement to the paleon- 
tologist, who is often obliged to determine a species of fossil fish on the evidence 
of a few detached scales’. 
Fishes of all these orders are found in the cretaceous period, and most of their 
parts, not only the teeth, vertebra, ribs and various bones of the head, but the 
fins, tail, and defensive bones, sometimes even the skin, are beautifully preserved’. 
The chalk fish have a nearer relationship to those of the tertiary period than to 
those of the oolite or older formations. The Edaphodontide of the chalk and 
eocene periods are very closely allied, as Sir Philip Egerton has pointed out. 
1 The first order he has denominated Placoid, from 7Aaé, a broad plate. These scales are some- 
times of large size, though occasionally in small points, as in the Shark and Ray families. 
The second order, Ganoid, from yavos, splendour; these scales are usually of an angular form, 
strong, and covered with a thick layer of enamel: the Sturgeon is an example. 
The third order, Ctenoid, from kveis, a comb; these scales are toothed or pectinated on their poste- 
rior margin like a comb; they are sharp and disagreeable to the touch: the Perch belongs to this 
order. 
The fourth order, Cycloid, from kv«dos, a circle ; the edges of these scales are smooth ; the external 
surface, like the Ctenoid, is often ornamented with markings. The Salmon and Herring are of this 
order. 
2 “Some fishes have teeth attached to all the bones that assist in forming the cavity of the mouth 
and pharynx, to the intermaxillary, maxillary and palatine bones, the vomer, the tongue, the branchial 
arches supporting the gills and the pharyngeal bones; sometimes the teeth are uniform in shape on 
the various bones, at others differing. One or more of these bones are sometimes without teeth of 
any sort, and there are fishes that have no teeth whatever on any of them. The teeth are named ac- 
cording to the bone upon which they are placed, and are referred to as maxillary, intermaxillary, pala- 
tine, vomerine, &c., depending upon their position.”— Yarrell’s Introduction to Recent British Fishes, 
pages 19 and 20. 
