MEMBRANIPORELLA. 199 



bright smooth fronds of which are sometimes dotted over 

 with its compact little pearly patches, in company with 

 the ubiquitous Microporella ciliata. In deeper water it 

 is found on shells. 



There is a graphic description of this species by its 

 accomplished discoverer, the late Mrs. Gatty, in Dr. 

 Landsborough's ' Popular History of British Zoophytes/ 



Genus MEMBRANIPORELLA (part), Smitt. 



Der. Dim. of Membranipora, a genus of Polyzoa. 



BKRUUCKA (part.), Fleming. 



LEPRXLIA (part), Johnston and Gray : Busk : &c. 



MEUBKA.MPORA (part.), Smitt 



MsMBRAJiroHBLLA (part), Smitt, Floridan Bryoz. pt. ii. 10. 



GENERIC CHARACTER. ZOARIUM incrusting, or rising 

 into free , foliaceous expansions, with a single layer of cells. 

 ZCKECIA closed in front by a number of flattened calcareous 

 ribs more or less consolidated. 



THIS genus has been constituted for a group of forms 

 (well represented by Lepralia nitida of authors) which may 

 be regarded as intermediate between Membranipora and 

 the Lepralia of Johnston. The passage of the one type 

 into the other may be clearly traced in the history of the 

 species just named. In its earlier condition Membrani- 

 porella nitida closely resembles one of the spiniferous 

 Membranipora. The front is completely closed by a 

 membranous roof; and the ribs of the adult state are 

 represented by suberect spines set round the margin. As 

 growth proceeds the spines bend inwards and increase in 

 size, and gradually take on the flattened, rib-like appear- 

 ance. After a time the opposite rows meet in the centre 

 of the cell-area, and the extremities, which are often en- 

 larged, are soldered together, so as to form a well-marked 

 median line. In some instances the ribs also unite latcrallv 



