153 



Onychocella Jullien^ 



Orjychocellidae Jullien. 



(PI. XXII, figs. 3 a— 3 d, pi. XXIV, fig. 10). 



The frontal calcification of the zooecia exclusively consists of a more or less 

 developed, depressed cryptocyst. No spines. The operculum is sometimes a wholly 

 chitinized simple operculum, sometimes a membranous opercular valve, and it is 

 generally surrounded by an arch-like, chitinized thickening of the frontal mem- 

 brane. The oblique, frontally ascending terminal walls are like the lateral walls 

 two-layered, and both kinds of walls are provided with a few multiporous rosette- 

 plates. The avicularia are independent (vicarious), with a strongly developed 

 cryptocyst and a flagellum-like, lengthened mandible which has a single or 

 double, thin, wing-like expansion. The ocecia, which may, I think, be considered 

 endozooecial, appear as low, not strongly prominent, swellings from the proximal 

 end of the distal zooecium, and they are separated on either side from the raised 

 mai-gin of the proximal zooecium by a suture. 



This genus is plentifully represented in the chalk-period, while only a small 

 number of recent species are known. 



It will be noticed that the above diagnosis corresponds not only with the 

 genus Onychocella Jullien, but with the bulk of his family Onychocellidae, the 

 latter comprising also a number of species, which must be referred to the new 

 family Membranicellariidae set up by me. Although I have no doubt, that in time 

 it will be necessary to acknowledge Jullien's family Onychocellidae, I shall at 

 present refer these forms to a single genus, as they are not yet so well known, 

 that the genus can be divided in a natural way. Jullien has set up no less 

 than eight genera, all of which however seem to me to be based on rather un- 

 important differences. 



Of this genus I have examined six recent species, among which one from 

 Denmark Strait, solida Nordg I The latter possesses a simple, membranous oper- 

 cular valve, while the others have a wholly chitinized, simple operculum, and 

 this difference is in the examined species connected with another. The fact is 

 that the free margin of the operculum is in all of them surrounded by an arched 

 chitinous sclerite, but while in the five species this chitinous arch only reaches 

 as far as the proximal corner of the operculum, it is in solida Nordg. contin- 

 ued a long way on the proximal side of the latter and here serves as base of 

 attachment for a parietal muscle. With the exception of Onychocella Luciae Jullien 



' 42,. p. 7, " 84 b, p. 8, 



