538 DE. A. W. ROWE ON THE GENUS MICRASTER. [Aug. 1 899, 



SO far as the special features of the test are concerned. Owing to 

 their greater bulk and breadth, however, there are certain small 

 differences between them, but they are purely the outcome of in- 

 creased size and breadth. For instance, the labrum and labral 

 plate are broader, and the periplastronal area more developed, in 

 the former ; also the sutures of the periplastronal plates are very 

 marked, giving a lyre-shaped arrangement of grooves, which is 

 sometimes very prominent. 



(6) Group of Micr aster cor-anguinum auctorum. 

 M. cor-anguimim (Leske) 1778.^ 



Excellent figures of the general appearance of the test may be seen 

 in Wright's ' Brit. Cret. Echinod.' Aionogr. Pal. Soc, pi. Ixii, and in 

 Eorbes's Dec. Geol. Surv. iii, pi. x. It is not proposed to review 

 minutely this group m the present paper, but for the sake of necessary 

 comparison the high-zonal features are tabulated and contrasted 

 with the low-zonal characters on p. 516. In addition a series of 

 profile-forms are shown in PL XXXV, line vi; the paired ambulacra 

 are figured in PI. XXXVI, figs. 7 & 8 ; the single ambulacrum in 

 PI. XXXVII, fig. 5 ; and the features of the base are brought out 

 in PI. XXXVII, fig. 9. Only examples from the upper two-thirds 

 of the M. cor-anguinum-zone have been considered in this bection, as 

 the lower-third of the zone has been referred to under the heading 

 of M. prcecursor. 



The type-form of this group is figured in PI. XXXV, line vi, 

 fig. 5, and it is, of course, the forma carinata of the higii-zoual 

 series, which has been worked up to as a maximum of caiinal 

 development through all the carinated forms in the low-zonal 

 M. 'prcBCursor-^TOiw, as shown in lines ii & iv. No. 4. The a. tual 

 maximum of carinal development is seen in M. rostratus, Mantell, 

 which was figured from the Brighton Chalk. The present writer 

 has met with this particular form only in the zone of Marsupites 

 testudinarius. This high-zonal carinated form is the type of the 

 high-zonal series, just as the ioima planidorsnta of the M. prcecursor- 

 group is the type of the low-zonal series. Allowing for the difierence 

 of horizon, with the necessary evolution of special features of the 

 test, the profile-shapes in the high- zonal series are the counterpart 

 of those in the low-zonal series, for we have forms resembling the 

 very depressed forma Normannice^ the flat-arched forma plani^ 

 dorsata, the round-arched forma heonensis, the forma carinata, and 

 the forma gibhosa. M. cor-anguinum is every whit as prone to 

 profile-variation as its low-zonal ancestor M. prcecursor. 



It will be unnecessary again to allude in detail to the photo- 

 micrographs of the special features of the test, as they have 

 already been commented on, by way of contrast, in the section 

 on the special features of the test, and in the Tabular Summary 

 on pp. 512-513. 



1 Leske, ' Addit. ad Kleinii Disp. Echin.' 1778, p. 221. 



