O74 Reviews—British Museum Oatalogues— 
obviously closer with the Cestraciontide than with any other 
recognized family.” Hight species of Motidanus—the only fossil 
genus known with certainty—are registered, the species ranging from 
the Jurassic rocks to the Red Crag inclusive. 
The CocHLioponTIpDm come next—‘“an imperfectly definable 
family, apparently related to the Cestraciontide, but with a more 
specialized dentition.” The group is restricted to the Carboniferous 
period, and includes many of Agassiz’s Cestraciont genera. Of the 
nine species of Helodus originally named by Agassiz, only one (H. 
simplea), from the Coal-measures, remains, the others being variously 
distributed. We then have an innovation, a new generic name, 
Pleuroplax, as being more appropriate, is substituted for Plewrodus. 
Psephodus follows with two new species (P. salopiensis and P. 
dubius). A British species, Sandalodus° Morrisii, from Oreton, 
appears to be the largest of the genus. In addition to the above 
named, the following genera are included in the family: Tomodus, 
Xystrodus, Deltodus, Poecilodus, Cochliodus, Streblodus, Deltoptychius, 
Diplacodus, and Cyrtonodus. New species of Deliodus (D. gibbus 
and D. rugosus), and one of Cyrtonodus (C. Hornet), are added. 
The Crsrraciontipm as here defined form an important group of 
fifteen genera and about seventy species. Of these only three 
genera (Orodus, Strophodus, and Acrodus) originally assigned by 
Agassiz to the family remain. The teeth are described as being 
“mostly obtuse, never fused into continuous plates; several series 
simultaneously in function;” and “no distinctive characteristics 
of value having yet been discovered, the so-called OropontTIpm and 
Hysopontip# are included in the family.” Its fossil representatives 
first appear in the Lower Carboniferous, and occur in more or less 
abundance in all the succeeding periods to the Chalk inclusive, 
the living Port Jackson Shark being the last survivor of the group. 
One of the earlier forms, Sphenacanthus costellatus, described by Dr. 
Traquair, is known by a fairly complete fish in the Museum having 
both dorsal spines in natural position; the other Carboniferous 
forms being mainly represented by detached teeth and fin spines. 
Hybodus is probably the most completely known genus of the 
family. lLiassic and Wealden specimens in the collection show 
interesting portions of the cranial structure, the internal skeleton 
and the external form; also the dermal covering, the hooked cephalic 
spines (Sphenonchus), and the dorsal fin spines, each in their respective 
positions. Moreover, in its close ally Acrodus, the arrangement 
of the dentition is observed. Portions of nearly complete jaws of 
each genus with the teeth in natural apposition are figured. 
The numerous Oolitic teeth named Strophodus are now practically 
known to belong to the Ichthyodorulites named Asteracanthus by 
Agassiz; Strophodus, however, being provisionally retained for the 
teeth not correlated with spines. The teeth named respectively 
S. reticulatus and S. subreticulatus have been found associated with 
the dorsal fin-spines of Asteracanthus ornatissimus, which name they 
now bear; Owen’s S. medius is also a synonym. The author has 
discovered that the species was armed with cephalic spines resembling 
