F. R. C. Reed— New Crustacea, Isle of Wight. 115 



margin of the articular ends of the centra. The costoids in the middle 

 of the tail are rod-like elements, decreasing rapidly in size backwards. 

 There is a great resemblance to the middle caudal vertebrae in 

 St. ungulatus. 



The distal caudals in St. prisons, as shown in Figs. 3c, d, are still 

 more elongate than the middle ones. The centrum is laterally 

 compressed, as Fig. 3c shows, and exhibits a pentagonal section, with 

 the point of the pentagon turned downwards. The articular surface 

 for the chevron bone on these vertebrae is only developed at the 

 posterior end. The concavity of the articular surface is also more 

 marked at this end than at the other. The neural arch in these 

 vertebrae, as in all the anterior ones, covers nearly the whole of the 

 neural canal; the elongate rod-like prezygapophyses are comparatively 

 feeble, their articular facets are directed as in the middle dorsals. 

 The narrow neural spine (Fig. 3d) rises in a remarkable manner 

 straight upwards ; it is blade-like, tapering towards its summit, and, 

 like the rest of this vertebra, it is characterized by the complete 

 want of rugosities, thus indicating clearly that on this bone no great 

 mass of firmly adhering tissue was present during life. This latter 

 observation will prove to be of the utmost importance when we discuss 

 the dermal armour of St. prisons. 



The distal caudal in St. prisons differs from that of St. ungulatus 

 and Diracodon by the feeble development of the neural spine, and still 

 more by the development of elongate post-zygapophyses, for these ai'e 

 quite short and nearly sessile on the blade of the neural spine in 

 St. ungulatus, Diracodon, and many other Dinosaurs, though not in 

 Polacanthus. The development of the neural spine and the post- 

 zygapophyses in St. prisons are features so strange for a posterior 

 caudal that if the shape of the centra did not prove beyond all doubt 

 the contrary, one might hesitate to refer this vertebra to an Omosaurus. 

 The biconcave nature of all the caudals of our Stegosaurus, and the 

 neural spines overlapping each other, do not imply great flexibility of 

 this organ. 



{To be concluded in our next Number.) 



III. — Sedgwick Museum .Notes, 

 xnew Crustacea, from the Lower Greensand of the Isle of Wight. 



By F. E. Cowper Eeed, M.A., F.G.S. 

 (PLATE VII.) 



AMONGST the large series of specimens of Meyeria recently 

 obtained by the Sedgwick Museum, Cambridge, from the Lower 

 Greensand of Atherfield, Isle of "Wight, two new and strange forms, 

 obviously referable to another genus, were detected by me in looking 

 over the material. Their interest consists not only in belonging to 

 new species but in representing the genus Thenops, of which the best 

 known and only British species, so far described, is Th. scyllariformis, 

 Bell, from the London Clay. There is one imperfect specimen in the 

 British Museum from the Speeton Clay attributed (with a query) 

 to Thenops, but no other British representative from the Cretaceous 

 appears to have been found. 



