162 Rev. T. Hincks's Critical Notes 



having founded his genus SteganoporeUa on the dithalamic 

 condition of the zooecium *. 



It woukl be pleasant to associate Dr. Jullien with this 

 group, which he has so ably investigated, by adopting his 

 name Onychocellida^ ; but the scope of this family is much 

 more restricted than that of the division which I propose, and 

 further it is mainly based on a character (the structure of 

 the avicularia) to which I find myself unable to attach the 

 significance which he does. 



5. Family SteganoporellidaB. 

 Fam. char. — Zoiecia closed by a membranous wall which 

 carries the orifice and operculum, divided by a horizontal 

 calcareous lamina, with a large variously-shaped opening 

 (opesia) at the upper end, into two compartments, in the 

 lower of which the polypide is lodged. 



In the family thus constituted two principal groups are 

 distinguishable. In one the aboral chamber is simple and 

 undivided ; in the other the inferior portion of it is shut off 

 by a diaphragm from the upper, with which it communicates 

 by means of a tubular passage ; and in this lowest room of 

 the somewhat complex structure the polypide is lodged. Of 

 the first group we have a typical member in Memhranipora 

 antiqua^^w&k [OiiycJwcella antiqua, Jullien), whilst the second 

 is well represented by Memhranijiora magnilahris, Busk [Stega- 

 noporeUa magnilahris, Smitt). 



In the second division, however, it will be necessary to 

 create two genera, for there are important structural differ- 

 ences between such species as S.magnilahrisandS.Neozelanicaj 

 Busk, and S. Bozieri, Audouin (sp.), which have hitherto been 

 included in the same generic group. 



In S. magnilahris f the whole of the upper half of the cell 

 forms in fact one large cavity, part of it above and part below 

 the opesia, which is closed in by the very large operculum 

 and the membranous front wall connected with it. 



The tubular orifice of the polypide-cell opens out within 

 the infra-laminar compartment, and a broad, shield-like 

 denticle rises in front of it. But in S. Rozieri^ Audouin 

 (sp.), and allied species this denticular process is continued 

 upwards, and unites with the margin of the cell, thus forming 

 an orifice with a thickened rim, arched above and produced 

 below. The upper half of this orifice (which is a kind of 

 second opening to the polypide-cell) is closed by the oper- 

 culum ; the lower half remains open, but is overspread by the 

 membranous front wall. By the structural modification just 

 • ' Floridan Bryozoa,' part 2, page 15. 

 t ' British Museum Catalogue ' (Busk), pi. Ixv. fig. 4. 



