Prof. R. Owen on rare Extinct Vertebrates. o 3 



incomplete on this side) ; f, an opening in the fan, left between 



two diverging ribs. From a photograph. 

 Fig. 2. Section across the base of fig. 1 (magnified about 50 diameters). 

 Fig. 3. Large acuate of the intermediate layer. 

 Fig. 4. Dumbbell-like spicule of the base or axis. 

 Fig. 5. Spined echinating acuate. 

 Fig. 0. Needle-like spicule of the dermal layer. The head is a little too 



inflated to be normal. 

 Fig. 7. Equianchorate and tricurvate spicules of the sarcode. 

 Figs. 3-7 all magnified 140 diameters. 



Plate VII. 



Varieties of the spicules of P. plena. 



Fig. 8. Common variety of the large acuate, with a spinose head. 



Fig. 9. Common variety of the large acuate with the distal end rounded 



off. 

 Fig. 10. A similar but extremely stunted form. 

 Fig. 11. A variety intermediate between those of figs. 9. 10. 

 Fig. 12. A young form of the large acuate, with spined head. 

 Fig. 13. A nearly spineless variety of the echinating acuate. 

 Fig. 14. Similar, but with a larger number of spines. 

 Fig. 15. Spined acuate, bent abruptly to one side. 



Figs. 8-15 are all magnified 140 diameters. 

 Figs. 16, 17. Normal forms of spined echinating acuates (x 435). 

 Fig. 18. Large smooth acuate, bent upon itself hook-like (x 140). 

 Fig. 19. Flesh-spicules. «, equianchorates ; b, tricurvates. X 435. 

 Fig. 20. Dermal spicule with both ends inflated and microspined 



(X 435). 

 Fig. 21. Short stout form of axial or dumbbell spicule. 

 Fig. 22. Attenuated form of the same spicide. 

 Fig. 23. Same kind of spicule bent upon itself at right angles. 

 Fig. 24. Same spicule, doubly inflated at one end. 

 Fig. 25. Same spicule, with one end rounded oft' and produced into a 



blunt mucrone. 

 Fig. 26. Similar, but without the mucrone. 



Figs. 21-26 all magnified 140 diameters. 

 Fig. 27. Head of a dermal spicule, magnified 435 diameters, to show the 



minute spines. 

 Fig. 28. Ordinary dermal needle (x 140). 

 Fig. 29. Normal dumbbell form (x 435). 



V. — On the Occurrence in North America of rare Extinct 

 Vertebrates found frag mentarily in England. — No. 2. By 

 Prof. R. Owen, C.B., F.R.S., &c 



[Plate VIIL] 

 [Continued from ser. 5, vol. ii. p. 223.] 



Part III. Restoration of Lewdon anceps. 

 In the section on Mosasauroids, in the " Report on British 



