Vol. 54.] MH. A. J. JUKES-BROWNE ON HOLASTER ALTITS. 



249 



most echinologists would not have hesitated to regard the two 

 extremes as distinct species. 



The following are the dimensions, in millimetres, of a series 

 of seven specimens from Wilmington, the last being exceptionally 

 large : — 





Length. 



Breadth. 



Height. 



No. 1 



22 

 26 



27 

 30 

 30 

 35 

 38 



20 

 24 

 25 

 25 

 28 

 31 

 35 



18 

 19 

 19 

 23 

 24 

 23 

 27 



No. 2 



No. 3 



No. 4 



No. 5 



No. 6 



No. 7 



Dr. Wright, in his * British Cretaceous Echinodermata ' (Pal. Soc. 

 Monogr. p. 319), entered the name of Holaster alius, Ag., as a 

 synonym of H. suhglohosus, but he does not mention it in his 

 description of that species, nor elsewhere in his monograph, so 

 that one can only conclude that he had no knowledge of its occur- 

 rence in England. Prof. E. Porbes ^ drew up a table of comparative 

 dimensions of Holaster suhglobosus, and this is reproduced by 

 Wright; the smallest specimen recorded therein has nearly the 

 same proportions as the largest of the series given above. 



Dr. Wright ^ describes a species under the name of Holaster suh- 

 orbicularis, which, however, is certainly not the suhorbicularis of 

 Defrance, Brongniart, or Goldfuss. He says that it is plentiful in 

 the Chalk Marl and Chloritic Marl ; but there must be some mistake 

 about this, as I have only seen one or two specimens that might 

 belong to it. It differs from all varieties of ff. altus in the flatness 

 of both the upper and lower surfaces, in its lesser height, and in 

 having a much larger vent. 



I will therefore conclude by pointing out the principal points in 

 which Holaster altus differs from H. suhglobosus : — 



(1) In its outline, which is oval, while subglobosus is often 



as broad as it is long. 



(2) In the posterior truncation of the test, while subglobosus 



tends to become cordiform and bluntly pointed posteriorly. 



(3) In the marked posterior sulcus, which is slight or absent in 



the other. 



(4) By its excentric apex, that of a typical subglobosus being sub- 



central. The position of the apex, however, varies much. 



(5) By the horizontality of the apical and posterior ridge. 



(6) By the deeper anterior sulcus, which is bounded on each side 



by a slight carina, more marked in some than in others. 



^ Mem. Geol. Surv. dee. iv, text to pi. vii. 



* ' Brit. Cret. Echinodermata,' Pal. Sec. Monogr. p. 314. 



