PENTAGONASTER MEGALOPLAX. 29 
adambulacral plates is also noteworthy. This seems to indicate the former 
presence of a distinct furrow series of spinelets or granules much smaller than 
usual, followed by granules or spinelets borne on the outer part of the plate, 
more irregularly placed than in the other forms described, and articulated on 
punctured eminences. 
The example which is represented in fig. 4a also has a narrower marginal 
border of infero-marginal plates than the type. The punctation of the infero- 
marginal plates is smaller than in the type, and does not present the striking 
scrobiculate character noticed in that example. The markings are rather to 
be described as lipped pits, and some granules are still in situ. The actinal 
intermediate plates do not have the retiform and crenulate ornamentation shown 
in the plates belonging to the specimen figured in 3a, but the margins of the 
punctations are strongly lipped. The supero-marginal plates are less regular 
and much less high than in the type specimen, but they are not perfectly 
preserved. 
Dimensions.—In the type specimen (figured on Pl. IV, fig. 2a) the major 
radius is about 41 mm., and the minor radius 26mm. Breadth of a ray between 
the third and fourth infero-marginal plates, counting from the median interradial 
line, about 12 mm. or rather more. Thickness of the margin about 8°5 mm. 
The specimen given in fig. 3a has a major radius of about 39 mm. and a 
minor radius of 24 mm. 
The specimen given in fig. 4a has a major radius of about 41 mm. and a 
minor radius of 25:5 mm. Breadth of the ray between the third and fourth 
infero-marginal plates about 11 to 12 mm., or rather more. 
Locality and Stratigraphical Position.—The type specimen, which is now pre- 
served in the British Museum, is labelled from the ‘‘ Lower Chalk” of “ Sussex,”’ 
but is stated by Forbes to have been obtained from the Upper Chalk. Other 
examples of the species have been collected from the Upper Chalk of Bromley, 
Sittingbourne, Purfleet, Gravesend, Sussex, and Wiltshire. Fine series are pre- 
served in the British Museum and in the Museum of Practical Geology, Jermyn 
Street. 
History.—The specimen which I have taken as the type of this species was 
originally referred by Forbes to the Asterias lunatus of Woodward, and was 
figured by him as that species in Dixon’s ‘Geology and Fossils of the Tertiary 
and Cretaceous Formations of Sussex’ (pl. xxiii, fig. 9). The same example is 
carefully represented on Pl. IV, fig. 2 a, of this memoir. 
5 
