10 



Escharina spinifera, the two large distal projections which appear in a number 

 of species of the genus Thalamoporella (PI. Via, figs. 4 a, 5 a) and the two corre- 

 sponding projections in the genus Claviporella (PI. XX, fig. 10 a). Undoubtedly also, 

 the very long and thin spines which appear at the edge of the calcified, arched frontal 

 wall of ^Lepralia'^ Poissoni in a very unusual way, belong to this division, and also 

 the likewise long and thin spines whicli somewhat scattered and in great numbers 

 surround the anter of the aperture in •> Schizoporellai. biserialis Hincks ', and 

 which give the impression of having been formed round a number of the nume- 

 rous scattered pores which appear in this species, in the same way as the very 

 short arched projections which occasionally appear round ocecial pores, for in- 

 stance, in the species of the genus Claviporella. The true acropetal spines like the 

 marginal ones are always formed by a Gymnocj'st, but in Porella (?) cornuta (PI. 

 XVIII, fig. 6 a) the endoocecium in a number of zooecia is furnished with one or 

 more hollow spine-like processes which in the same manner as the acropetal 

 spines have a ring-like origin and are no doubt formed by chalk-particles depos- 

 ited under the membranous ectoeoecium. These projections, however, are in no 

 inner connection with the ooecium and cannot therefore be looked upon as true 

 spines. 



3) The bilaminate spines, which have hitherto only been found in the family 

 Catenariidce and will be more fully spoken of under this family, spring from the 

 free margin of a more or less developed sinus (the sternal sinus), from the margin 

 of which also an inner. Cryptocyst lamina takes its origin. As these spines issue 

 from a margin in which a Gymnocyst and a Ci-yptocyst meet, they must of 

 course be two-layered, their outer layer being formed by the Gymnocyst and the 

 inner by the Cryptocyst. They attain Iheir highest development in the genus 

 Costicella (PI. XII, figs. 1 a— 1 d, PI. XX, figs. 8 a— 8 b, fig. 9 a). 



The morphology of the zooecium. 



As is known we can in the cheilostomatous Brijozoa distinguish between six, 

 as a rule well-separated, walls, namely, the two lateral, the two terminal, the 

 basal and the frontal. It is generally difficult however to distinguish exactly 

 between the lateral walls and the frontal wall (or basal wall) in species which 

 appear in single rows, and in those zooecia which arise by superficial gemmation 

 and in most cases in more or less erect position (for instance in the Cellepora 

 and. Holoporella species) only the basal wall is sharply bounded, the other walls 



' 30, p. 250. 



