METOPASTER PARKlNSOiNI. 35 



their surface is traversed by four or five ridges running parallel to the auibulacral 

 furrow, with punctures upon which the spinelets composing the armature were 

 articulated. There were four or five spinelets in each lineal series. The spinelets 

 are short, their length being about equal to the length of the plate, stumpy, com- 

 pressed, slightly tapering and rounded at the extremity ; and all appear to have 

 been uniform. 



The actiiial intermediate plates are rather large for the genus ; those adjacent to 

 the adambulacral plates are pentagonal in form, but elsewhere they are subhexagonal, 

 or perhaps more correctly polygonal. The plates are very large on the inner 

 portion of the area, but diminish greatly in size at the outer margin of the disk 

 adjacent to the marginal plates. The surface of the intermediate plates is entirely 

 covered with small, equidistant punctations, upon which a uniform close granulation 

 was previously attached. Remains of this granulation are still occasionally to be 

 seen in situ on plates here and there in the example under notice. Entrenched 

 pedicellaritB similar to those above described on tlie plates of the abactinal surface 

 occur on a number of the plates in the series adjacent to the adambulacral plates, 

 but the organ does not appear to diverge, or only very rarely, from the normal 

 form of a central foramen and two lateral trenches. 



Dimensions. — In the specimen figured on PI, X, fig. 2 a, the major radius is 

 38 mm., and the minor radius 30 mm. Other examples have the following 

 approximate measurements : R = 85 mm., r = 27 mm. ; E, = 43 mm., r = 34 mm. 

 The diameter of the disk (R -|- r) in well-grown tests ranges, therefore, from 

 60 mm. to 80 mm. The thickness of the margin is about 11"75 mm. 



Localitif and Stratigrapldcal Position. — All the examples figured in this 

 Monograph were obtained from the Upper Chalk, near Bromley. The species is 

 a characteristic Upper Chalk fossil in the south of England, and has been found 

 in beds of that age at Brighton, Charlton, Gravesend, Kent, and other localities. 

 It is stated by Forbes to occur in the Lower Chalk of Sussex, but I have not seen 

 any examples from that horizon. 



Historij. — A fossil starfish which has been generally considered to bo this 

 species was figured by Parkinson in his * Organic Remains of a Former World,' 

 vol. iii, pi. i, fig. 3, but it was referred by that author to the Pentagonaster 

 regularis of Linck. The last named has, however, been supposed to be a recent 

 species, but the type has unfortunately been lost, and the form has not subse- 

 quently been recognised definitely. Apart from this the fossil starfishes now 

 under notice are certainly distinct from the form indicated by Linck's figure, and 

 this view was taken by Forbes, who named the species after Parkinson in his 

 memoir ' On the Asteriada; found fossil in British Strata,' and figures of the 



