M. K. A. Zittel on Fossil Calcispongice. 61 



the enamelled crown is borne upon an enormously developed 

 cemental root, to which conical mass it sometimes appears as 



a mere apex* 



EXPLANATION OF PLATE VIII. 



Fig. 1. Restoration of Leiodon anceps, Ow., as shown by an outline of the 

 skeleton, omitting certain of the estimated numbers of the con- 

 stituent types of vertebrae, for lack of space. 



Fit/. 2. Side view of atlas vertebra. 



Fig. 3. „ axis vertebra. 



Fig. 4. „ cervical vertebra. 



Fig. 5. „ dorsal vertebra (first type). 



Fig. 6. „ dorsal vertebra (second type). 



Fig. 7. „ dorsal vertebra (third type). 



Fig. 8. „ lumbar vertebra. 



Fig. 9. Front view of caudal vertebra (first type). 



Fig. 10. Side view of caudal vertebra (second type). 



Fig. 11. Front view of caudal vertebra (third type). 



Fig. 12. „ terminal caudal vertebra. 



Fig. 13. Bones of right antebrachium and fin. 



Fig. 14. Portion of dermal scutation of the side of the trunk. 



Fig. 15. Outline of transverse sections of maxillary tooth. «, root : 

 b, crown. 

 (All the figures, save 14 and 15, are much reduced in size.) 



VI. — Studies on Fossil Sponges. — V. Calcispongice.. 

 By Kael Alfred Zittel. 



[Continued from vol. iii. p. 379.] 

 Revision of the Fossil Calcispongio?. 



Family 1. Ascones, Hackel. 



Stomach-wall thin, penetrated by inconstant cutaneous 

 pores, wall-less and temporary openings in the parenchyma. 

 Skeletal spicules usually in a single layer parallel to the 

 surface. 



No fossil representatives at present known. 



Family 2. Leucones. 



Stomach-wall thick, irregularly traversed by curved, 

 branched, usually anastomosing canals, running without any 

 definite arrangement. Parenchyma-skeleton consisting of 



* See ' Monograph on British Fossil Cetacea,' p. 12, pi. 1. fig. 5, a, in 

 the volume (4to) of the Palreontographical Society issued in 1870. 



