38 



spine, which as is known appears in very different degrees of development in a 

 number of members of this family. As a similar enclosure of- the operculum is 

 also found in Menipea clausa Busk ', Men. Jeffreysi Norman ^ and Scrupocellaria mar- 

 supiata Jull.^, it seems probable that the operculum in these species has a similar 

 structure. Besides in the species just mentioned, we find an independent opercular 

 valve in the Coilostegous genera Micropora and Cellularia, and in the genera of the 

 division Ascophora: Microporella , Inversiula, Onchopora, Urceolipora, Chorizopora, 

 Haplopoma, Adeonellopsis and Tiibiicellaria. While we may briefly call such an 

 operculum as appears in most of the Malacostega an opercular valve, I would 

 propose the designation » simple operculum* for any opercular valve, which is 

 distinctly marked off from the frontal membrane, and can consequently be isolated 

 as an independent formation. While the proximal edge of such an operculum 

 forms as a rule a straight line it is more or less concave in a number of species of 

 the genera Cellularia and Thalamoporella, so that the hinge-line falls a little proxi- 

 mally to the edge, and in such cases the simple operculum does not fill the 

 whole zooecial aperture, the proximal part of which is filled by a membrane. 

 Within the division Ascophora the same thing appears in a new form from Singa- 

 pore belonging to the family Petraliidae. Jul lien* has founded a genus: Cha- 

 peria, the species of which were formerly referred partly to Membranipora, and 

 partly to Monoporella, and Waters^ says regarding this genus: »This group was 

 indicated by Jul lien under the name of Chaperia, but while he based it upon 

 two lateral plates, which I have shown are for the attachment of the opercular 

 muscles, and do not occur in all species, the important character is the form of 

 the operculum, whicH is separable, and which has at each side an elongate pro- 

 tuberance for the attachment of the muscles.« In opposition to Waters I would 

 maintain that the most important generic character is the two plates mentioned, 

 which I have found in all species I have examined, whereas the operculum 

 according to my investigations is subject to a fairly considerable variation. As 

 Waters refers both Memb. galeata and Memb. cristata to Ch. annulus Manz., we 

 must, before speaking about the operculum in the different forms, make the ad- 

 mission that, our material is too small to venture on expressing an opinion as to the 

 identity of the two last-mentioned forms, which in any case are very closely con- 

 nected. In a species, which under the name of Memb. cristata has been sent me 

 by Miss Jelly and which came from South Africa, the opercular valve occupies 

 nearly the whole of the distal half of the large oval aperture of the zooecium, 

 and is in its proximal portion furnished within each lateral rim with a very 



' 8, p. 20; 2 80, p. 446; » 43, p. 507; * 45, p. 61; <■ 112, p. 655. 



