the surface, all the others end either in a new pore or in another sutural line. In 

 Crisia eburnea the calcification takes place in narrow longitudinal belts, and a 

 similar mode of calcification is seen in the short and wide hollow protuberances, 

 which are situated on each side of the aperture in several Thalamoporella (PI. 

 VI a, figs. 4 a,^ 5 a). Besides the form of striping, which is due to lines of growth, 

 and which for instance is often very distinct in the Hippothoa species, the basal 

 wall especially of the zocecia often presents a distinct, longitudinal or fan-shaped 

 striping which is most probably due to the arrangement of the separate lime 

 particles. This form of striping is widely distributed in the species BicellariidcE 

 and Scrupocellariida;. 



Before leaving this subject I must shortly mention an apparent observation 

 made by Nitsche', according to which the calcified frame of every zooecium of 

 Membr. membranacea after boiling in alkali is divided into three pieces, namely, 

 in two double-folded end pieces each consisting of a terminal partition wall 

 and a piece of the adjoining side-wall, as also of two lateral pieces. This view 

 is nevertheless not correct. After boiling like this more or fewer zocecia in a col- 

 ony may indeed show cracks or bendings, but these are quite accidental, and 

 not an expression for the mode of calcification of the zocecia. 



Cryptocyst and Gymnocyst. 



Under the generic name Onychocella JuUien^ has described several recent 

 species of a type which had a great extension in the seas of the chalk period 

 but which only has a small quantitj' of now living representatives. As is the 

 case in a Flustra species, the whole of the frontal wall is covered with a mem- 

 brane in which can be seen an opercular valve, but when we remove this mem- 

 branous cover we find underneath it and separated from it by a distinct space 

 a more or less concave calcareous layer, which distally has a semicircular aper- 

 ture (opesia) through which the polypide . can make its way out. This aperture 

 which was formerly regarded as the orifice of the zooecium in the fossil species is 

 consequently separated by a space from the real orifice, which is situated in the 

 covering membrane. In contrast to the membranous ectocyst Jullien designates 

 this deeper-lying calcareous ectocyst as a Cryptocyst, and proposes on the basis of 

 this observation to divide the cheilostomatous Bryozoa into two divisions, according 

 to the presence of a single or double ectocyst. To the first division: Monodennata, 

 he refers such forms as Eschara foliacea, Lepralia hyalina, L. coccinea, Cellepora 

 pumicosa and Flustra foliacea, and to the other division: Diplodermata, besides 



' 80, p. 42; " 42. 



