ELORIDAN BRYOZOA. 41 



But in all oiir classifications of a truly natural group, where the different species 

 will be ärran ged into more or less coinplete series, we must be prepared for seeing the 

 limits between the divisions fading away, especially, when the developmental changes 

 are known. Thus, the 



Hippothoa Hyndmanni a ) 



with almost the same right would be placed in the preceding genus, what will be evi- 

 dent, in considering the Floridan variety, in wellgrown specimens, taken by Pourtales, 

 west off Tortugas, growing on a dead shell and on a JSfullipora, from the depths of 

 42 and 68 fathoms. On account of sotne differences from the British form, with the 

 following characterisation, I give it a new naine, 



Hippothoa porösa (Pl. VII, fig. 158). 



Char.: Apertimi zoceciorum, margine secundario elevato circumvallata, marginem 

 proximalem primariuui primo concavum, quamvis e sinu mediano ad sinum utrumque 

 lateralein convexe arcuatur, postremo rectum praäbet. Zocecia plana poris dense positis 

 perforantur, vibraculario magno laterali muniuntur, cujus apertura ad partem distalem 

 zooacii locuin tenet. 



Hab.: E profundo 40 — 70 orgyarum colonias quasdam hujus formaj Nulliporam 

 et testarn mortuam insidentes ad Floridam cepit Pourtales. 



As the most important differences, for its distinction from the true Hippothoa 

 Hyndmanni, as far as I know that form, the fiatter shape of the zocecia as well as 

 their punctation, all över their front, by pores, and the more distal place of the vibra- 

 cular opening are to be regarded, although even these differences are very common as 

 variations for the species of the Mvriozoidan as well as of the Eschariporidan series 2 ). 

 The figures by Johnston and Busk, furthermore, mark the pores along the margins of 

 the zocecia much greater, than what we see on the Floridan form, but even there, in 

 the younger zocecia, these great pores are to be observed, although, usually, at last 

 they seem to be closed by the proceeding calcification. Very often I have found one 

 of these pores for a longer time remaining open, closed only by a membranous covering. 



The margin of the vibracular aperture, on its outer side, is raised in its middle, 

 almost alike what we have seen on the Cupularice, whereby the vibraculum, which, 

 when entire, has the length of 3 or 4 zooecia, in its bend över the zocecium, is moved 

 more obliquely över this. 



A very interesting observation on the developmental changes of the zooecial aper- 

 ture here may be made. At first, the proximal part of that aperture has the same con- 

 striction at the articulation of the operculum, as in the preceding genus, a correspon- 



') Leprcdia Hyndmanni, Johnst., Brit. Zooph., ed. 2, p. 306, tab. LIV fig. 6; Gray (Rerentia) List Brit. 



Anim., part. 1, Rad., p. 122: Busk (Lepralia) Cat. Polyz. Brit. Mus., part. 2, p. 74. tab. LXXXVII, 



figg. 5-8; Norman, Brit. Assoc. 1868, Rep., p. 307. 

 2 ) C fr. Ofvers. Vet. Akad. Förh., 1867, Bih., pag. 102 etc., on Hippothoa vulgaris. 



K. Vet. Akad. Hanill. B. 11. N:o i. O 



