20 F. A. SMITT, 



These measurements, of course, only can have a relative value, but, commonly, 

 as they show, the zooecia of B. tuberculata, are smaller and, relatively, broader. 



In their outer appearance, the two forms very easily can be distinguished, but 

 regard being had to the developmental changes, the question yet stånds open, if not 

 the above-named differences will be accounted for by the different localities and man- 

 ners of growing. 



The specimens taken by Pourtalbs were brought up from 10 fathoms. 



Biflustra Savartii') (Pl. IV, figs. 92—95). 



The inconstancy of the tubercles of the preceding species may justify the de- 

 termination of this species, at tirst given by Busk. Our Floridan form, no doubt, is 

 identical with the Membranipora Savartii from the Crag Formation, described by that 

 anthor, and, like this, it entirely wants the tubercles, which are shown in the Sa- 

 viGNY'an figure cited below. 



The very uniform granulation on the front side (the above-named lamina), which 

 slopes clown, from the margins, inwards to the secondary area, commonly arranges 

 itself in transverse rows, though not very regular, and here and there in the elliptical, 

 secondary area, it projects into denticles, very like those of Bifl. tuberculata, although 

 the}? never seem to be so closely set together. 



That great "serrate denticle within the lower margin" on Bifl. delicatula, described 

 by Busk, I never saw on Bifl. Savartii, except that a few times, in that place, a broad 

 projection was to be seen, which I hold to be the ocecion of the nearest older zocecion 

 in the same row, placed in the same manner as, for instance, on Flustra truncata, 

 where the ocecia, totally immersed, intrude into the proximal end of the nearest younger 

 zocecion. 



Another difference from the Bifl. delicatula would be the appearance of the back 

 side of the colony; for there, on the B. Savartii, we see the zocecia (fig. 94) almost 

 quite plain, forming very regular rectangles, instead of sharp ridges, as figured by 

 Busk. But this difference, perhaps, will be accounted for, in connexion with a higher 

 calcification, by the inore or less intimate connexion of the two opposite layers of the colony. 



As to their size, the zocecia vary as much as in the preceding species; among 

 the variations I measured one zocecion, which seemed to be of the most common and 

 regular shape, 0,-i mm. in length, 0,3 mm. in its greatest breadth. 



The specimens, which were sent me for examination, all dead, Avere taken by 

 Pourtales at a depth of 29 fathoms. They are all raised in that form, which, by 



') ? Flustra Savartii, Aud., Sav., Descript. de VEgypte, Polyp., tab. X, fig. 10; D'Oeb. (Membranipora) Pal. 

 Franc, Terr. Crét., vol. V, p. 542. (Membranipora corrugata, Blnvlle, Diet. Se. Nat., vol. LX, p. 412) 

 ? Flustrellaria tubulosa, I)'Okb., Pal. Franc, 1. c. p. 532, tab. 727, figg. 9, 10. 

 ? Membranipora Ligeriensis, D'Orb., 1. c., p. 550, tab. 607, figg. 5, 6. 

 Membranipora Lacroixii, Busk, Gat. Brit. Mus, Polyz., tab. 104, fig. 1. 

 Membranipora Savartii, Busk, Crag Polyzoa, p. 31, tab. II, fig. 6. 

 ? Biflustra delicatula, Busk, ibid., p. 72, tab. I, figg. 1. 2, 4; tab. II, fig. 7. 



