PALEONTOLOGY. 131 



paratory to the formation of a new layer, the old surface was 

 covered by a coating of vesicles to serve as an under structure for 

 the support of the new, carefully finished, calycinal floor. The 

 radial plications of the calyces generally unite in the centre into a 

 papillose projection ; in rare cases they die out before reaching the 

 centre and leave a small naked spot within. The arrangement of 

 the. lamellae into four fascicles and the development of a small 

 septal fovea are not unfrequently noticeable in the bottom of the 

 cells ; the steeply ascending sides of the inner pit are surrounded 

 by crest-like plications, which grow stouter as they bend over upon 

 the expanded marginal parts, and, in their course to the margin, 

 repeatedly divide into narrow rounded rugae, often five or six 

 times more numerous than the crests of the cell pit from which they 

 emanate. The division in this case is not conformable with the 

 rule of intercalation of new lamellae set forth in the introductory 

 pages, but takes place apparently without any strict order. The 

 plications of this expanded peripheral area are mere superficial 

 rugae, and do not combine into vertical lamellae. In several species 

 on each side of a radial ruga of the expanded calycinal surface, a 

 row of punctif orm, closely approximated pores opens, which are in 

 alternating position on the two sides ; in perfectly intact surfaces 

 these pores seem to^ be closed ; it is only in slightly worn speci- 

 mens that they are open circular orifices. 



STROMBODES PENTAGONUS, Goldfuss. 



Strombodes striatus, D'Orbigny. 



Large discoid expansions covered on the lower side with a con- 

 centrically wrinkled epitheca, and attached at the central apex. 

 Surface of disks composed of irregularly polygonal, shallow calyces 

 with an abrupt central depression. Diameter of the calyces very 

 variable in different specimens, ranging from one to four centi- 

 meters. The steep walls of the inner cell pit are surrounded by 

 about thirty stout, crest-like plications, which, reduced to a smaller 

 number by coalescence, unite in the centre, and form there a styli- 

 form protuberance ; or the bottom of the cell remains even while 



