15 



In the species belonging to the genus Electra (E. pilosa, E. verticillata, E. bellula etc.) 

 we find a good-sized Gymnocyst, and the Cryptocyst is either quite lacking or is 

 represented only by a very slight margin within the spines. In the genus Callo- 

 pora a cryptocyst is developed in very varying degree and in C. lineata, C. cra- 

 ticala, C. Dumerili and C. aurita 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. Flemingi and C. trifolium it has grown to such an extent that the 

 zooecium has only a little trifoliate aperture. Hi neks calls it in such species 

 »an inner lamina*. Finally, the calcified part of the frontal wall in Memb. arc- 

 tica, M. Rosseli, M. cornigera etc. is only formed by a Cryptocyst, as is also the 

 case in the species referred to the genera Onychocella 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 Cribrilina annulata, 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 Gattyce and Cr. chlitridiata among recent forms are perhaps 

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

 proximal part may here sometimes reach the same length as the area. The area 

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

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

 within this division, only in species of Membraniporella as a narrow marginal 

 region round the membranous area of the aperture. 



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

 the families Chlidoniidae, Alysidiidae, Cellulariidae, Microporidae, Steganoporellidae 

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

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

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

 and as a rule separated 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 Monodermata, 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. 166. 



