PLATE XL 



Fig, 1. Portion of the lower side of the disk, showing a part of the white [ilute ss, with the ramifications 

 of tlie liver II, and the course of the tubules tt, which have passed through the white plate, 

 with portions of the corrugations of the lower side of the circular chambers c. 



Fig. 2. Diagrammatic sketch showing the relative position of the disk, of the edge of the white plate, and 

 of the mantle. 



Fig. 3. Central chamber a, with the adjoining chambers from which lead the first rows of tubules t. 



Fig. 4. ('luster of tubules on the dorsal side of the white plate. 



Fig. 5. Corrugations of three of the inner chambers of the lower side of the disk, showing the short 

 tubules and their mode of attachment, about under the white plate. 



Figs. 6, 6'. Greatly enlarged view of a few joints of one of tlie tubules. 



Fig. 7. Part of the outer portion of the disk, showing the arrangement of the stigmata u, on the upper 

 surface. 



Fig. 8. Slightly oblique view of the cross-section of the outer part of the disk showing the position of the 

 stigmata oo,. of the successive chambers aa, and of the primary and secondary corrugations on 

 the lower side, c and c', of the circular chambers, and tlie mode of attachment of the 

 tubules tt. 



Fig. 9, Different profile view of a portion of the disk. Lettering as before. 



Fig, 10, Shows the general arrangement of the simple corrugations, c, of the lower side of the circular 

 chambers, in a young specimen. 



Fig. 11, Portion of the lower side of the disk showing the folds of the lower side of the chambers, t (', as 

 older far as the last outer circular wall, ppp, of the disk. 



Fig. 12. Portion of the disk of a young Porpita, -^J' in diameter, with four circular chambers ; o'-o*, stig- 

 mata, j[/', fold in the chambers corresponding to the original eight chambers, and forming in 

 older specimens the irregularly radiating lines of the upper side of the disk,- 



Fig, 13, Slightly obliipie end view of a part of the corrugations, c c', of the last eharabei^of the edge of 

 the disk. 



Fig. 14. An end \'iew of a few corrugations of a similar part of the disk. 



