68 FOSSIL ASTEROIDEA. 



from Mitraster Eiuiteri and M. rngatiis. A further distinctive feature is the size 

 of the distal paired plate. This plate is triangular. The base of the triangle 

 measures 2*7 mm., giving the plate twice the length of the more proximal plates. 

 The plate is gibbous at its outer extremity as in M. Hnnteri. All the plates are 

 ornamented with a single or double marginal row of small spinelets. The ocular 

 is a small conical plate barely visible in abactinal -saew. It fits into notches on 

 the lower surface of the distal paired plates, and is, as usual, notched on its 

 inferior surface for the purpose of protecting the unpaired terminal tube foot. 



The median infero-marginal plates are rather longer than the corresponding 

 members of the superior series. The first two, reckoning from the median inter- 

 radial line, are 1-85 mm. long, and 8-5 mm. broad. The third is only 1"8 mm. long 

 and not quite as broad. The fourth has approximately the same length l)ut is 

 subtriangular in form. The fifth is a small triangular plate. Two infero-marginals 

 and a portion of a third are situated underneath the distal paired supero-marginal 

 plate. 



The veutro-lateralia visible are small hexagonal plates covered Avith a fine uniform 

 granulation. The adambulacralia are small oblong plates. The margin of the disc 

 is very abrupt, but the transition from infero-marginalia to the actinal surface is 

 more gradual than that of the supero-marginalia to the upper surface. A number 

 of small granules are irregularly distributed between tlie plates. 



Eemarlcs. — Unfortunately, the specimen is slightly distorted, so that the pro- 

 nouncedly cycloidal appearance in the figure is partially due to the unnatural 

 position of the marginal plates, which has brought the inferior series into the dorsal 

 view. The supero-marginal plates appear to have been straight and the inferior 

 series but slightly cycloidal. This, together with the large comparative size of 

 the ultimate paired plate, would bring the species very near to the genus Meto- 

 jxister. Forbes remarked upon the fact that it appeared to be intermediate between 

 Goniaster {Mdopaster, Sladen) nncains and Guiiiastt'r (Mitraste); Sladen) nigatiis. I 

 have therefore considerable doubt as to the validity of the separation of these two 



genera. 



Localitij and Stratignijihical Fosifioi>. — Upper Chalk of Haughton, Sussex. 



