Asterospondt/li. 



21 



Table-cases, 

 Nos. 27/28. 



of Lyme Regis and the Wealden of Pevensey Bay, Sussex. 

 Palwospinax, ivonx the Lower Lias of Lyme Regis, and the 

 Upper Lias of Wiirtemberg, is a small fish with smooth dorsal 

 fin-spines and simple constricted vertebrae ; Synechodtis, of 

 Cretaceous age, is almost identical. Acrodus, ranging from the 

 Muschelkalk to the Grault, only differs from Hyhodus in the less 

 cuspidate character of its teeth (Fig. 122). Asferacavthus, with 

 a dentition commonly named Strophodus (Fig. 124), is proved by 

 specimens in the collection to dift'ei" only from Acrodus in the No. 29. 

 pattern on its teeth and fin-spines. Fine examples of its head- 

 spines (Sphenoiichus) , from the Oxford Clay of Peterborough, 

 are exhibited ; while a jaw in a block of Great Oolite from Caen, 

 Normandy (Fig. 124), is unique. It will be observed that the 

 front prehensile teeth in Hyhodus, Acrodus, and Asteracantlius 

 (StropJiodus), are relatively larger and less numerous than those 



Table-case, 



Fig. 124. — Jaw of Asteracantlius {StrophoOvs laedius, Owen; ; Great Oolite, Caen, Normandy. 



of Cestraciou. The latter genus seems to range from the Upper 

 Jurassic to the present day. 



An interesting Cai'boniferous family of which little is known 

 beyond the dentition, is that of the Cochliodontidte, apparently 

 closely related to the Cestracionts. Their jaw is arranged 

 somewhat like that of Cestraciou, but the several series of 

 lateral teeth are each represented by a single plate, coiling 

 inwards by growth at the outei- edge. Cochliodus (Fig. 125) 

 is the typical genus, and Streblodns, Psephodus, Sandalodv.s, 

 Poecilodus, etc., are very similar forms. Many of the teeth 

 named Helodus pertain to the symphysis of the jaw of these 

 fishes ; and in one genus, Pleuroplaiv, from the Lower Carboni- 

 ferous and Coal Measures, such teeth are only imperfectly fused 

 together in the plates. 



Table-case, 

 No. 30. 



