15 



In tlie species belonging to (he genus Electra (E. pHosa, K. vcrticHUila, E. bellnUi etc.) 

 we find a good-sized Gymnocyst, and the Cryptocyst is either (}iiite lacking or is 

 represented only by a veiy slight margin within the spines. In the genus Cullo- 

 pora a cryptocyst is developed in \ery varying degree and in C. lineuia, C. cra- 

 ticiild, C Diiinerili and C aiirila it is represented only by a slight granular 

 margin in the circumference of the membranous area, while in other species as 

 e. g. in C. Flemiu(ji and C. trifoliiim it has grown to such an extent that the 

 zod'cium lias only a little trifoliate aperture. Hi neks calls it in such s|)ecies 

 »an inner lamina«. Finally, the calcified part of the frontal wall in Mcnib. (irc- 

 tica, M. Rosseli, M. cornigerd etc. is only I'oimed by a Cryptocyst, as is also the 

 case in the species referred to the genera Oiujchocella and Chaperia. 



The Gymnocyst may attain a very different degree of development in the 

 forms of the family Cribrilinidae, and its development is naturally in inverse 

 proportion to the extent of the characteristic area, which consists of two rows of mu- 

 tually connected spines. While this area in some forms, e. g. Membraniporella nitida 

 and Cribriliiia annuhitn, constitutes the whole or almost the whole of the frontal wall, 

 a smaller or larger part of the latter is in other species formed by the true Gym- 

 nocyst. Cribrilina Gattya- and Cr. chlitridiata among recent forms are perhaps 

 those in which the Gymnocyst reaches its largest relative development, and its 

 proximal |)art may here sometimes reach the same length as the area. The area 

 is of still smaller extent, and almost to be regarded as rudimentaiy in some 

 species from the Danish cretaceous formation. A Cryptocyst seems to appear, 

 within this division, only in species of Membrani-porella as a narrow niarginal 

 region round the menil)ranous area of the aperture. 



In the forms which we have called >coilostegous«, namely, in the members of 

 the families Chlidoniidae, Ahjsidiidae, Cellulariidae, Microporidae, SleyanoporeUidae 

 and ThalamoporelUdae, the frontal wall is formed by a depressed Cryptocyst, but in 

 the last of these families the two marginal regions, which hound the opening 

 distally and which often end in arched protuberances, are formed by a Gymnocyst 

 and as a rule sej)arated from the Cryptocyst by a well-marked boundary line. 



The numerous families belonging to the division of Ascophora all have an 

 arched calcified frontal wall, and as previously noted JuUien refers the repre- 

 sentatives of this division, mentioned by him, to the Monndcrimda, by which he 

 understands those forms which have no Cryptocyst. Calvet' however, for a 

 number of these forms has proved that the arched calcified frontal wall is in 

 reality a Cryptocyst, and according to my investigations this is the case with 



■ 9, p. 16(i. 



