326 SIDNEY F. HARWEK. 



Oue or two colonies of M. impressa (S. Devon) are par- 

 ticularly interesting in having a Scliizoporelliform ancestrula. 



In Scliizoporella vulgaris (Naples) I have found an 

 ancestrula (fig. G), like that of Microporella ciliata, with 

 ten marginal spines and a calcified plate {crypt.) which is 

 probably a cryptocyst. This resembles the cases which I 

 have described as " intermediate" between the typical Tata 

 form (fig. 2) and the adult condition with a completely 

 calcified frontal wall. It appears to me that these " inter- 

 mediate " Tata forms deserve special attention. It remains 

 to be seen whether the calcified plate internal to the circlet 

 of spines is really a cryptocyst or not. Taking into considera- 

 tion the frequency of the occurrence of a cryptocyst in the 

 Amphiblestrum group of Membranipora (although 

 the morphology of this part has yet to be determined in many 

 of these cases) and in such a typical Membranipora as 

 M. delicatula^ Busk (e. g.) — and noticing, moreover, the 

 presumed occurrence of a cryptocyst in Bicellaria grandis 

 (fig. 1), — the presumption appears to be that the plate uuirked 

 crypt, in fig. 6 is really a cryptocyst. The bearing of these 

 cases on the phylogeny of the Cheilostomata is considered in 

 a later part of this paper (p. 3o4). 



Cribrilina radiata/ Moll. — The study of a young colony 

 of this species has led me to altogether unexpected conclu- 

 sions, which probably indicate that this species is not really a 

 Cribrilina at all. The ancestrula (fig. 7) is a Tata form 

 with eleven marginal spines, of which theproximal {sc.) is broad 

 and somewhat scutum-like, lying horizontally over the frontal 

 membrane, while the others are erect or somewhat reclined 

 outwards. Each of the erect spines bears a minute calcareous, 

 denticulated lobe which originates about halfway up the spine, 

 and lies horizontally, directed inwards over the frontal mem- 

 brane. The outline of the ancestrula is somewhat concealed 

 by the basal lobes of the younger zocecia. 



Two zocEcia in contact with the ancestrula are smaller than 

 the rest, and are doubtless those which were first formed by 

 ' Uiiicks, ' Bnt. Mar. i'ol.,' ISSO, p. 1S5. 



