518 DE. A. W. KOWE ON THE GENUS MICRASTEK. [Aug. 1 899, 



M. cor-anguinum yar. latior, as they are here considered merely as 

 broad varieties respectively of M.prcecursor and of M. cor-anguinum 

 auctorum (see footnote p. 530). The reasons for establishing a 

 separate Group for M. cor-bovis and M, Leskei will be set fortii 

 in the description of these species. 



(1) Group of Micr aster cor-bovis. 

 M. cor-bovis, Eorbes, 1850. 



In Dixon's * Geology of Sussex,' 1st ed. (1850) p. 342, pi. xxiv, 

 figs. 3 & 4, Eorbes describes this large form as ovate and slightly 

 cordate, with a depressed upper surface, the highest point being 

 in the anterior segment. He describes the apical disc as anterior, 

 the anteal sulcus as shallow, the ambulacra as moderately excavated 

 (the posterior being half the length of the anterior), and the 

 primary tubercles on the dorsal and ventral plates as much scat- 

 tered, and small for the size of the test. 



Length = 76 mm. ; breadth = Qb mm. ; height = 45 mm. 



In the Decades Geol. Surv. iii. p. 9, Forbes mentions, in addition, 

 that the mouth is small, and the central area of the ambulacra 

 smooth. 



Cotteau, ' Echinides fossiles de I'Yonne,' vol. ii, p. 352, looks upon 

 this species as a large variety of M. Leslcei, and he dismisses the 

 subject in a few lines, for he sees no reason to preserve it as a 

 species. From his remarks it is clear that he could not have 

 handled many examples, as he mentions hardly any of the salient 

 features of this strongly-defined species. 



Wright (' Brit. Cret. Echinod.' Monogr. Pal. Soc. p. 276) gives 

 merely a verbatim, copy of Forbes's text, and the only original observa- 

 tion which he offers is that the anus is in the middle of the obtusely 

 subtruncate border. In this he is mistaken, for it occupies the usual 

 position towards the top of the posterior truncation. He gives, 

 however, an admirable plate of the large form described by Forbes, 

 in pi. Ixii A, figs. 1, 2 a Sib. These figures the present writer would 

 accept as correctly defining the naked-eye appearances of the test^ 

 and for this reason no other general figure is given in this paper. 

 In PL XXXV, line ii, of this paper, a large example is photographed,, 

 to show the typical profile of the large form of this species, and to 

 serve as a contrast to the much commoner smaller forms which are 

 depicted in line i, Nos. 1 to 4. 



Like Cotteau, Wright also looked upon M. co7'-bovis as a gigantic 

 variety of M. Leskei, but it is reasonable to infer that his acquaint- 

 ance with the species was inconsiderable, as he ignored the examples 

 of smaller size, and failed to note many important features of the 

 test. It may be mentioned also that most authors have had a 

 misconception of Forbes's type, and have generally confounded it 

 with M. Leskei. 



It will, therefore, be evident that considerable difference of 

 opinion has existed in the case of this Micraster, and that, for so* 



