8 F. A. SMITT, 



In comparing it with the Membranipora spinosa, D'Orb. x ), from Peru and Bolivia, 

 one will scarcely find any difference, for that number of spines (18 — 20), cited by him, 

 even the Floridan form presents on some of its older zooecia, and, in particular in its 

 overgrown parts, it totally resembles the D'Orbign)'an figure. 



The avicularia (fig. 62) are scattered in the interstices between the area?, where 

 the limits between the zooecia are very obscure. 



When we remember the developmental changes of this species, it will be easy 

 to understand its relation to the 



Membranipora irregularis 2 ) (Pl. II, fig. 63), 



of what form Pouetales has taken two small colonies, from 60 fathoms at Florida, 

 the one growing on a Nullipora, the other on a shell of a died Pecten. 



It is of a very simple construction, wanting all other secondary buddings than 

 the ooecia, which in their form 3 ) show its near affinity to the preceding. The wan- 

 ting of the spines would do nothing as to the specifical distinction, and it would be 

 the same with the more firmly calcificated nature of the walls of its zooecia; but this 

 calcification, in the most calcified zooecia, below the covering membrane of the area», 

 produces an inner "expansion all round the circumference, but Avider inferiorly". This 

 last character brings it nearer to the unicornis-Y&ri&tion of this type, where it must be 

 regardcd, I think, as one of those reductions of the secondary buddings, which are very 

 common in the Membraniporidan series 4 ). 



The borders of the area? sometimes are roughly granulated, although nothing 

 near so much, as what shows the figure given by Busk 5 ). 



The small specimens, I have had for examination, do not allow me to say much 

 about the variability of the M. irregularis ; but once, I think, it will be demonstrated, with 

 more certainty, to be only a developmental stage of the Membranipora unicornis. That 

 same judgment, without any hesitation, we must give of the interesting form, 



Membranipora sigillata G ) (Pl. II, figs. 64 — 68) 



which, for the first time, was described by Pouetales, as brought up from 270 fathoms 

 off Havana. Yet that specimen was only a small fragment; but since then he has found 

 the species again, in a more complete colony (fig. 66), living at the depth of 262 

 fathoms, at Florida. 



It is growing in the manner of Retepora (auctt.), and this so perfectly alike, 

 that it would be irapossible to separate it from that genus, were it not for the totally 

 different zooecial constitution. In connexion with the Reteporidan manner of growth, 



x ) Voy., ibid., pag. 16, tab. VIII, figs. 1-4. 



2 ) D'Orb., 1. c. pag. 17, tab. VIII, figs. 5 and 6. 



3 ) I measured the bveadth of one ooecion to about 0,2 4 mra. 



4 ) Öfvers. Vet. Akad. Förh. 1867, pp. 419 and 473. 



5 ) Quart. Journ. Micr. Se., N. Ser., vol. VII, Zooph., pl. XXXIII, fig. 3. 



Obs. IVOrbtgny says: "cellulis . . . margine loevigato cinctis". 



8 ) Cellepora sigillata, Pourt., Bull. Mus. Comp. Zoöl. Cambr., N:o 6, pag. 110. 



