a General History of the Marine Poli/zoa. 87 



slight spinous elevation on the margin of the lamina. Prof. 

 Smitt (though doubtful) is inclined to identify his Floridan 

 species with M. tuberculata, Bosc * ; but this, though be- 

 longing to the same group and exhibiting the same general 

 facies, is, in my judgment, essentially distinct. I shall give 

 hereafter figures of M. tuberculata, which I have from various 

 parts of the Atlantic and also from California. In M. deli- 

 catula the form of the cell is normally quadrangular and elon- 

 gate ; but there are many irregularities : very commonly the 

 angles are obliterated above, and the upper part of the cell is 

 rounded ; there are also diversities in size. The nodules at 

 the upper angles of the aperture are very inconstant ; they 

 sometimes occur on only a few cells in a colony ; at best they 

 are rather small blunt knobs. 



The genus Biflustra was originated by D'Orbigny and 

 adopted by Busk for forms with a Membraniporidan cell and an 

 erect foliaceous or ramose growth ; that is, it was constituted 

 to represent a mere variation in colonial habit. Smitt has 

 retained the name, but with a very different and, it seems to 

 me, rather vague application. He says, " The quadrangular 

 shape of the zooecia, as well as their strong, unusually high, 

 and hardly calcificated and granular margins, in most cases 

 will make the Biflustridan type recognizable." He also 

 remarks that " the most striking characteristic for this family 

 .... will be the relatively great size of the zooecia " (Flor. 

 Bryoz. pt. 2, p. 17). These characters, I confess, seem to me 

 to be much too vague and unimportant to stand as the 

 criteria of a family group ; whilst, on the other hand, D'Or- 

 bigny's generic diagnosis, though definite enough, being based 

 on mere colonial habit, and not on any difference in the 

 structure of the zocecium, can hardly be maintained, if the 

 later views of Polyzoan classification are sound. For the 

 present I shall rank the species of Biflustra (both of Busk 

 and Smitt) under Membranipora. 



? Membranvpora trifolium, S. Wood, var. minor. 

 (PL XI. fig. 6.) 



Zooecia somewhat pyriform, slightly narrowed above, ex- 

 panded in the middle and tapering off below, closely united ; 

 the lower half of the area filled in by a granulated lamina, which 

 is carried up on each side of the aperture, where it is slightly 

 crenate; aperture obscurely trifoliate, margins scarcely raised, 

 not beaded. Frequently a small avicularium on the lower 



* Floridan Bryozoa, pt. 2, p. 18. lie expressly states, however, that 

 he leaves "the question yet undecided. 



