82 FOSSIL ASTEROIDEA. 



3. Pentacebos coeonatus, Forbes, sp. PI. XIX, figs. 1, la; PI. XXIV, figs. 2, 



2 a, 2 b, 2 c ; PI. XXV, fig. 9. 



Oreastee coeonatus, Forbes, 1848. Mem. Geol. Suit. Gt. Brit., vol. ii, p. 467. 



— — Forbes, 1850. In Dixon's Geology and Fossils of the Ter- 



tiary and Cretaceous Formations of Sussex, pp. 327, 

 328, pi. xxi, fig. 7 a— d. 

 — Dajardin et Hup,', 1862. Hist, Nat. Zooph. Echin. (Suites 



a Buffon), p. 389. 



— — Forbes, 1878. In Dixon's Geology of Sussex (new edition, 



Jones), pp. 362, 370, pi. xxi, figs. 7, 7 a—d. 



Specific Characters. — Disc large, with conspicuous nodular primary radialia and 

 interradialia. The major radius is about five times the length of the minor radius. 

 Sides of arms very steep, so that the arm appears to be square in cross section. 

 A triple row of intermarginalia present in the interbrachial areas. 



Material. — The type specimen of this species is preserved in the British Museum 

 of Natural History (Dixon's Coll., 35480). Unfortunately, only one arm and a 

 portion of the disc are preserved. A further specimen, registered E. 2562, from the 

 cabinet of Mrs. Smith, of Tunbridge Wells, is preserved in the same museum, and 

 another example is to be seen in the Museum of Practical Geology, Jenny n Street. 



Description. — The most conspicuous feature of the disc is the circlet of ten 

 "large, more or less polygonal nodose pyramidal tubercles." 1 These are the 

 primary radialia and interradialia. The interradial tubercles are rather larger 

 than the radial tubercles, the former measuring 9*2 mm., the latter 7" 7 mm. in 

 diameter. The remainder of the disc is covered by irregularly shaped plates. 



The madreporite has been broken away from the disc of the specimen no. 35480. 

 It is figured Plate XXV, fig. 9. 



R : r : : 58 mm. : 19 -f~ mm. in the type specimen where the single arm is 

 broken short. In specimen no. E. 2562 R : r : : 100 mm. : 20 mm. The arms 

 are 30 mm. broad at the base. Their surface is flat, and the sides slope away 

 at right angles, so that a cross section of the arm is square. 



Both radial and adradial plates are present in the base of the ray. The 

 adradials are irregular in shape and soon disappear. The radials are roughly 

 oblong in appearance, and exist throughout that portion of the arm preserved. 

 They diminish in size, however, distally. 



The supero-marginal plates are indented on their anterior median surface. 

 1 Forbes, in Dixon's ' Geology of Sussex,' p. 327. 



