446 R. ETHERIDGE ON A TERTIARY HEMIPATAGUS. 



minutely granulated. The oral aperture is nearer the anterior end, 

 transverse and semilunar, with the margin of the ventral lip a little 

 thickened ; in weathered specimens a few pores of the two pairs of 

 ambulacra may be seen radiating from it. 



Obs. — In two specimens before me the primary tubercles on the 

 extreme anterior portion of the lateral pair of interambulacra are 

 confined to two rows only, whilst in a third specimen one tubercle 

 of the third row is developed, but the remainder are obsolete. The 

 peculiar pyriform plate (a, fig. 5) separating the posterior pair of 

 genital pores, corresponds to a similar plate well shown in an en- 

 larged figure of the apical disk of Spatangus purpureus, Mull.* 

 (a, fig. 9). It is there seen to be a prolongation backwards and an 

 enlargement of the right antero -lateral genital plate, and therefore 

 occupies a somewhat corresponding position to the Madreporiform 

 body in some of the Endocyclica, although posterior to the apical 

 disk instead of anterior. 



Affinities and Differences. — From H. Hofmanni, Goldf.f, our 

 species, as in the case of H. Forhesii, W. & D., is distinguished by 

 non-crenulate tubercles which, on the ventral surface of the test, 

 unite with the scrobicular circle, and by the much more convex form. 

 From H. Forhesii, W. & D., to which it bears the nearest resem- 

 blance, H. Woodsii is at once distinguished by the more convex 

 form, straighter and more truncate anterior end, and much more 

 overhanging posterior end, which slopes downwards more rapidly 

 than in H. Forhesii. In the latter the whole of the dorsal sur- 

 face is flattened and compressed, whereas in H. Woodsii it is 

 merely that portion immediately anterior to the apical disk. In the 

 last-named the primary tubercles are much less developed than in 

 H. Forhesii, in which they extend further along the lateral pair of 

 interambulacra than in the new species (see figs. 3 & 8), and, instead 

 of being confined to two rows only, form three and sometimes four. 

 From H. grignoniensis, Ag.J, the new species is distinguished by 

 its greater dimensions, more convex form, and apparently a larger 

 amount of tuberculatum on the ventral surface ; from H. tuber cu- 

 latus, Zittel§, by the same characters which separate it from H. 

 Forhesii, W. & D.||. Lastly, from H. prcelongus, Herklots^f, our 

 species is distinguished by the form in general, and the much smaller 

 number of primary tubercles. 



Locality and Geological Position. — The specimens of Hemipatagus 



* After Desor, ' Synopsis der Ech. Foss.' t. 44. fig. 1. 



t Petr. Germ. i. p. 152, t. 47. fig. 3, a, b, c ; Desor. * Synopsis,' p. 416, t. 44. 

 figs. 4, 5. 



X Desor. 1. c. p. 416 ; Forbes, Quart. Jour. Geol. Soc. viii. 1852, p. 342, 

 t. 18. fig. 7. 



§ Foss. Mollusk. u. Echin. aus Neu-Seeland, " Novara" Expd., Geol. Theil, 

 B. i. 2. Ab. p. 63, 1. 12. fig. 1. 



|| Both Dr. Zittel and Prof. Duncan remark on the very close similarity 

 existing between H. Forhesii, W. & D., and H. tuberadatus, Zitt. ; in fact, the 

 former remarks that, except in size, there is scarcely any difference (I. c. 

 p. 64). 



^[ Foss. de Java, Echinodermes, 1854, Spatangus, p. 11, pi. 2. fig. 6 ( = 

 Hemipatagus, Zittel, I. c. p. 63). 



