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 irregulai'ly placed than in the other forms described, and articulated on 

 punctured eminences. 



The example which is represented in fig. 4 a 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 3 a, but the margins of the 

 punctations are strongly lipped. The supero-marginal plates arc less regular 

 and much less high than in the type specimen, but they are not perfectly 

 preserved. 



Dimensions. — In the type specimen (figured on PI. IV, fig. 2 a) the major 

 radius is about 41 mm., and the minor radius 26 mm. 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 85 mm. 



The specimen given in fig. 3 a has a major radius of about 39 mm. and a 

 minor radius of 24 mm. 



The specimen given in fig. 4 a 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 ] 1 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, Purflect, G-ravesend, 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 ' (pi. xxiii, fig. 9), The same example is 

 carefully represented on PI, IV, fig. 2 a, of this memoir. 



5 



