114 R. ETHERIDGE, JUN., ON ASTROCRINITES 



Fig. 11. Dorsal view of fig. 5: a, one of the" pseudambulacra ; b, position of 

 the second pseudambulacrum ; c, apex of the third pseudambulacrum ; 

 d, base of the unsymmetrical lobe. 



Plate XIII. 



Fig. 12. Dorsal view of a rather elongately lobed specimen : a, dorso-central 

 plate pressed upwards ; b, the base of the unsymmetrical lobe ; c, c, c, 

 the three symmetrical lobes. 



13. Exterior view of the excentric-aperture plate : a, the pointed extre- 



mity received into the re-entering angle of the plate or plates. 



14. Interior view of the same : a, the pointed extremity ; b, circular cup- 



like depression on which the apex of the lid appears to rest, placed at 

 the end of the inward ridge seen at g, fig. 5 ; c, channel leading in- 

 wards from it ; d, folds into which the channel appears to break up. 



15. End view of the unsymmetrical lobe : a, the excentric-aperture plate 



(figs. 13 & 14 &c.) ; b b', the plate into which fits the excentric-aper- 

 ture plate, with the suture apparently dividing it into two ; c, lip of 

 the excentric-aperture plate. 



16. Interior view of the dorsal surface of a crushed-down specimen : a a', 



the plate or plates similar to b b' in fig. 15, crushed inwards ; b, b, b, 

 the three symmetrical dobes ; c, c, hollows of the interlobular plates 

 into which the apices of two of the pseudambulacra fit, similar to a, 

 figs. 7 & 7 * ; d, d, position of the other two interlobular spaces in the 

 perfect organism ; e, interior of the dorsal surface, with a thin cover- 

 ing of matrix. 



17. Enlarged view of a portion of one of the pseudambulacra: a, ambu- 

 lacral groove ; b, alternate, lateral short groove ; c, inner depression or 

 socket at end of b; d, outer depression or socket at end of groove / 

 proceeding inwards from the slit or opening e ; g, lateral plate, pro- 

 bably equivalent to the pore-plate in Pentremifes ; h, supplementary 

 plate, identical with the supplementary pore-plate in the same genus ? 



18. Diagrammatic view of the cross section of a pseudambulacrum: a, am- 



bulacral groove ; b, more or less horizontal portion of the pseudambula- 

 crum ; c, ridge forming an interspace between the inner pair of sockets ; 



d, exposed sides of the pseudambulacrum bent down at a considerable 

 angle ; e, concealed portion below the general surface of the organism. 



19. Side view of a pseudambulacrum : a, base ; b, apex ; c, exposed lateral 

 portion ; d, concealed lateral portion ; e, inward process. 



20. The excentric aperture and plates surrounding it : a, the more or less 



pyriform aperture ; b & c, the side plates which complete the aperture, 

 and which probably correspond to one of the spearhead plates of the 

 other lobes (a, fig. 3) ; the plate c is absent in the specimen, and its 

 position is therefore only indicated ; d, the excentric-aperture plate ; 



e, its lip ; /, pointed extremity of the plate which is received into the re- 

 entering angle of b b\ fig. 15 ; g, lid or valve filling-in the aperture. 



21 & 22. Tubercles of the arched and crested plates {b, fig. 5, and figs 8 & 9) 



23. Microscopic spine attached by matrix to one of the specimens. 



24. Small body (b) adhering to dorsal surface of fig. 3, supposed to be a 



Foraminifer ( Valvulina, sp.) ; a, tubercles of dorsal surface. 



25. Greatly enlarged view of a specimen of Valvulina, sp., for comparison 



with b, fig. 24. 



26. Dorsal surface of A. tetragonus, Austin, from a weathered specimen 

 kindly presented to me by Major Austin : a, cavity left by the dorso- 

 central plate, which has been accidentally removed ; b, b, the two 

 forked plates ; c, the unsymmetrical lobe. 



27. Pentremites cervinus, Hall (Geol. Eept. State Iowa, 1858, i. pt. 2. t. 25. 



f, 11 a): a, a, two of the radial plates ; b, suture between them. 



N.B. All the parts figured are magnified, their true size varying from T V inch 

 to ^ inch. Nos. 1 and 5, which are entii*e forms, are ^ inch in diameter. The 

 remainder are individual parts enlarged. 



