62 



XVIII, figs. i:ia, PI. XXIV, iig. 1,'i), besides in all nicinbers of the family Onclio- 

 poridae (Ft. XIII, figs. 6—9, PI. XXIV, iig. 12), and in both cases tlie wliole 

 frontal wall of the oa-ciuni is provided with such a layer, which is placed be- 

 tween the ecto- and endood'ciuni. There is however this dillerence thai while 

 this layer in Emballolhcca ari.ses high up from the cryplocysl of Ihe distal zocrciuui, 

 in the family Onchopoikkw it arises from the distal wall between Ihe two zocL'cia. 



We very often in species of the genus just mentioned meet with the very 

 peculiar case, that the ooecium is formed by three to five adjoining zoa'cia and 

 conse(iueiilly consists of the same number of segments meeting in sutures, of 

 which each single one includes a calcified endooa'cial layer, a cryplocyslic layer 

 and a membranous ectoooecial layer. 



We have seen that the basal wall of the od'cium in ScrupncelUtrui sc(tbr(i 

 arises by calcification of a part of the original frontal membrane of the zoci-cium, 

 and nearly one half of the hyperstomial ooecia might be in a similar relation 

 to the zooecium, even though the size of this common wall for the zoa-ciuni and 

 ooecium may be very variable in the diderenl forms and sometimes present 

 considerable dificrences in species of the same genus. It seems as a rule to be 

 large in the families Meinbrdiiiporidae, Scnipocelhiriiddc and Petniliidtie, as also in 

 the genera Eschardla, Escluiroiiles, Schizupurella, Ksclidrina and Microporellu, while 

 it is for example very small in Dendroheaiiia Miirraiianu (PI. IV, figs. 2 a — 2 e), 

 Porella compressa and Smitlind trispinosd. In the genus Smiltina especially the 

 relation between the zo(i3cium and the oa^cium seems to be subject to great 

 variations, and while the common wall in some species is large or of fairly con- 

 siderable size, e. g. in S. boreulis, S. Sinilti (PI. XIX, fig. 4 a), S. palmala (PI. 



XIX, fig. 5 a), it is as mentioned very small in .S. hispinosu, and may again l)e 

 quite lacking in other species (S. reticuUda, S. Laiisboroui, S. linearis). In Ihe 

 last case these oa-cia, which we may call indej)endeul, consist of Iwo layers in 

 their whole extent, and are formed by the ofrcial fold alone, while this fold in 

 the previously MHiilioned cases arises in Ihe circumference of a semi-circular area, 

 namely, the parlition-wall lielween Ihe zod-cium and the ooecium. Such inde- 

 pendent ocrcia seem to appear as a rule in Ihe families RicelUiriidde. Hcteporiddc, 

 Celleporidae, Mijriozoidde and Discoporidde, and they may also occur in llie genera 

 Smittiiid and Porella (c. g. in P. saccatn); but as already mentioned there is 

 no sharp distinction between independcril and dejiendent ocrcia, because the 

 parlilion-wall may vary considerably in size. While the independent Od'cia in Ihe 

 above-mentioned Smitliiia species allach themselves so closely lo the frontal wall 

 of Ihe distal zodcium, Ihal it is not jxissible to isolate llieni as a whole, the 

 hyperstomial (xecia in the laniily liicelldriidac on the ollu-r hand are freely pro- 



