ASTERACANTHUS. 



i; 



35 cm. ; more or less gently arched and laterally compressed, but not keeled 

 anteriorly ; posterior face slightly raised, Avitli denticles relatively smaller than in 

 the type species ; ornamental tubercles very numerous and closely arranged, 

 mostly oval in form, and not only forming longitudinal series but also tending to 

 arrangement in regular transverse series; 

 the tubercles more or less fused into longi- 

 tudinal ridges near the apex of the spine. 



De.i^cripflon of Specimens. — T\\q type 

 spine is well preserved, lacking only the 

 apex and the posterior denticles. The 

 specimen shown in Text-fig. 7 is still finer, 

 with the apex only a little worn and the 

 posterior denticles again lacking. The 

 rounded front border and the character- 

 istic ornament are especially well seen. 

 The posterior face is not sharply keeled, 

 but only gently rounded, and in some other 

 specimens in the British Museum its rather 

 small denticles are arranged in two well- 

 separated close series. The degree of cur- 

 vature varies, and some spines are nearly 

 straight, but all must have have been very 

 obliquely inserted. It seems impossible at 

 present to distinguish that of the anterior 

 from that of the posterior dorsal fin. 



Horizon and Localit)/. — Middle Purbeck 

 Beds : Swanage, Dorset. 



2. Asteracanthus semiverrucosus, Eger- 

 ton. Text-fit?. 8. 



Fju 8. — AsteracantMts semiverrucosus, Egerton ; im- 

 perfect dorsal fin-spine, left side view, in matrix, 

 two-tliirds nat. size. — Middle Purbeck Beds : Swan- 

 aoe, Dorset. Dorset County Musevini, Dorchester. 

 Aifter Egerton. 



1854. Agteraccmthus semiverrucosus, P. M. Gr. Eger- 

 ton, Aun. Mag. Nat. Hist. [2], vol. xiii, p. 43 i. 



1855. Asteracanthus semiverrucosus, P. M. G. Eger- 

 ton, Figs, and Descripts. Brit. Organic Remains 

 (Mem. Geol. Surv.), dec. viii, pi. iii. 



Ty/pe.— Imperfect dorsal fin-spine; Dorset County Museum, Dorchester. 



Specific Gharacfers.—BoY&iiX fin-spine about 26 cm. in length, much arched, 

 laterally compressed and keeled anteriorly; ornamental tubercles ovate, very 

 large, sparsely and rather irregularly arranged, some fused into longitudinal ribs. 



Description of Specimen.— The type spine of this species still remains unique 

 (Text-fig. 8). It lacks both the apex and much of the inserted base, but otherwise 



