562 MANUAL OF NATURAL HISTORY. 



with equal -lobed, or homocercal tails ; also fourteen 

 genera of placoid Cestraciontidce, with elongate 

 bodies and tessellated teeth, of which Acrodus is 

 one. The ganoid genera with homocercal tails, are 

 principally Lepidotus, Tetragonolepis, Dapedium, 

 Amblyurus, and Semionotus ; Chondrosteus, a 

 genus of Acipenseridm, or sturgeons, is also from 

 the Lias of Lyme-Regis. 



While all the lepidoid and sauroid fishes which 

 inhabited the seas before the deposition of the Lias 

 had the vertebral column prolonged into the upper 

 lobe of the tail, or were heterocercal, the fishes of the 

 Lias group, with the exception of the Coccolepis, 

 have the tail homocercal, like most of the fishes 

 living in the seas of the present era. 



The annulose animals found in this formation 

 belong to crustaceans of the genus Coleia; species of 

 Astacus, and minute entomostracous Oyprididce; 

 and, among insects, of coleopterous and orthop- 

 terous genera, including the beautiful neuropterous 

 dragon-fly, JEshna liassina, and the remains of air- 

 breathing annulose animals, cotemporaries of the 

 gigantic marine saurians. Of molluscous animals, 

 the Cephalopods were most abundant ; vast numbers 

 of Ammonites and Belemnites, several species of 

 Nautilus, and the pens of Loliginidce, have been 

 brought to light. Among the gasteropodous tribes, 

 we only meet with the genera Rotella and Pleuro- 

 tomaria — bivalves, belonging to the genera Gry- 

 phc&a, Cardinia,Lima,Avicula, and Hippopodium, 

 have been found in the lower Lias shales ; and 



