146 HEMIPEDINA. 



The spines, many of which are preserved in situ, are long and needle-shaped ; they are 

 shorter and stouter than those of Hemipedina Bechei (fig. 1 b), although the diameter of 

 the test of H. Bowerbankii greatly exceeds that of H. Bechei ; the spines of H. Bower- 

 bankii are three quarters of an inch in length ; the head does not taper much towards 

 the acetabulum (fig. 2 c) ; the milled ring is thick, but not so prominent as in H. Bechei ; 

 the stem likewise is thicker at the base, and tapers regularly to the point ; the surface 

 is deeply sculptured with fine longitudinal lines. 



Affinities and differences. — This species very much resembles Hemipedina Bechei, but 

 the imperfect condition of the test of that species renders a comparison of this part of the 

 body with that of II. Bowerbankii impossible ; the spines, however, of the two species, 

 which are drawn side by side on the plate (figs. 1 b, 2 c), show that these two nearly allied 

 forms from the same bed are, however, specifically distinct, the spine of H. Bechei being 

 longer and more slender than that of H. Bowerbankii, although the test to which it was 

 attached is smaller ; the milled ring in H. Bechei is narrower and more prominent, and 

 the head more conical, than the homologous parts in H. Bowerbankii. It resembles 

 Biadema seriate, Leymerie (PI. IX, fig. 3 a, b), from the Inferior Lias of France, which I 

 have copied * for the purpose of comparison, and likewise to show the probable form of our 

 Lias specimen. In this very rare urchin, the primary tubercles are larger (fig. 3 b), and 

 there are only two, nearly of the same size, abreast on each plate ; the scrobicular circles 

 are more complete (fig. 3 b), and the granulations fewer but more numerous ; the pores 

 are much closer set together in the zones, there being twelve pairs opposite each inter- 

 ambulacral plate. 



Locality and Stratigraphical position. — Hemipedina Bowerbankii was collected from 

 the marly beds of the Lower Lias, at Lyme Regis, by Mr. Bowerbank, to whose magni- 

 ficent collection it belongs. I have not ascertained the precise Ammonital zone in which 

 this urchin was found. I have great pleasure in dedicating this species to our amiable, 

 excellent, and indefatigable Secretary, to whose great and continued exertions, through a 

 series of years, the Palaeontographical Society owes much of its present success. 



Hkmipedina Jardinii, Wright. PI. IX, fig. 4 a, b, c, d, e,f. 



Hemipedina Jardinii. Wright, Annals and Magazine of Natural History, 2d series, 



vol. xvi, p. 96. 



Test small, much depressed ; ambulacral areas wide, with two rows of marginal 

 * 'Memoires de la Societe Geologique de France,' t. ii, p. 330, pi. 24, tig. 1, 1839. 



