300 Busk — Polyzoa of the London Clay. 



The species here represented belongs to the latter genns, and it is 

 somewhat remarkable though not difficult of explanation that in all 

 the specimens the posterior furrowed surface is that which is most 

 extensively exposed. 



In the Crag Polyzoa I have recorded the existence of a species 

 belonging to the genus Biflustra as thus defined, which so closely 

 resembles an existing species abounding in the Eastern seas from 

 China to Australia, and doubtless elsewhere, that I have ventured to 

 describe them as identical under the name of Biflustra delicatula. 

 The resemblance between this form and the one I am about now to 

 describe is so close, that in small fragments and in certain con- 

 ditions, it would be next to impossible to distinguish one from the 

 other. But closer and more extended observation will, I think, show 

 that they are specifically distinct. 



In the Eocene species the polyzoary seems to have grown in an 

 irregularly plicated, infundibuliform shape, probably not unlike that 

 of Biflustra meandrina of D'Orbigny (Paleont. Franc, p. 257, pi. 695, 

 fig. 7-10), and which may be likened to the mode of gi.'owth of 

 Betepora cellidosa and Beaniana, whilst in the recent form the growth 

 is more like that oi Eschar a foliacea, that is to say in large, foliaceous, 

 contorted expansions. And the Crag species would seem to have had 

 the same habit. Other differences are seen in the rather small size 

 of the cells ; in the more rounded form of the opening and more 

 especially in its being bordered below by a distinct thickened margin 

 whilst in B. delicatida that border is thin and sharp. From B. mean- 

 drina, D'Orbigny, it differs in the absence of the regular rhomboidal 

 areolation of the surface as well as in the thickened border of the 

 aperture. In B. marginata (PI. 696, fig. 1-4), D'Orbigny, the open- 

 ings appear to be oblong and the septa are not doubled as in the 

 London clay species — nor are they represented as granular, but there 

 may, nevertheless, be some reason for doubting whether the two are 

 really distinct ; for the present, however, I think, it will be safer so 

 to consider them. 



2. Glen. Biflustra, D'Orbigny. 

 B. eocena, PL XII. Fig. 2. 



B. cellulis ohlongis, supra arcuatis, septis granulosis, duplicibus ; aper- 

 turd suhrotundd, margine inferiori, incrassato, granulosa. Polyzoarium 

 suhinfundibidiforme. 



Cells, oblong arched above ; septa, granular double ; aperture, sub- 

 oval or rounded, the lower border thickened, granular : polyzoary, 

 irregularly infundibuliform. 



3. Fam. GEMELLABIADJE, Busk, Brit. Mus. Cat. p. 93. 



The family Gemellariadoe, as defined in the above place, comprises 

 all species having the cells in pairs, which do not form distinct 

 internodes separated by flexible joints, but constitute a continuous 

 dichotomously divided polyzoary. As hitherto known to me it con- 

 tains only forms having a flexible consistence, but the present in- 

 stance seems to show that that is not to be taken as an essential 

 character. 



