38 F. A. SMITT, 



rum libera erigitur, quare horum apertura supra frön tern stirpis elevata niargine libero, 

 setis saapissime quinque munito circumscribitur. Avicularia sat inagna, ad medium 

 frontem zooeciorum posita, irregulari ordine distributa, rostro supra frontem stirpis 

 eriguntur, quare aperturam ellipticam oblique ad planum frontis illius positam prsebent. 

 Ooecia rotunda calcificatione e lateribus surgente obducuntur. 



Hab.: Forma? striatulce coloniam, Nulliporam incrustantem, e prof. 68 orgyarum, 

 formam glabram e prof. 36 — 42 org. haud raram cepit Pourtales. 



As to the form of the zooecial apertures, here we, evidently, find the same ge- 

 neric character as in the two preceding species; but the constriction at the articulation 

 of the operculum is considerably greater, whereby the distal (opercular) part of the 

 aperture becomes more alike to a section of a circle than to that of an ellipse, and 

 the proximal part, especially the median sinus, groAvs narrower. This alteration of the 

 type, however, in connexion with the inarticulated stem, in the erected state, would 

 induce us to make it a new genus, if we knew any more species, which were to be 

 placed in a closer relation to the G. glabra; but now, with the perplexing richness of 

 genera, proposed for the Bryozoa, it seems to be more convenient to conjoin it with 

 its nearest known allies, although the horseshoe-shaped form of the zooecial aperture, 

 through the narrowness of the proximal part, by a good deal is gone away. 



Under the same specifical name I have conjoined two evidently distinct forms. 

 This is not the first time, and the real meaning, I hope, easily will be understood. 

 When some forms, either trough their developmental changes or through the union in 

 them of the most characteristic features, are connected with each other in the same 

 manner, as, in other species, we find the different parts of the same colony to be, then 

 I give a binomial navne to that group of forms, because, besides the intimate relation, 

 it is a matter of convenience to use a collective name, as in inany instances it will be 

 difficult, perhaps impossible, to decide, to what form any worn or incoraplete colony 

 will be referred. This, however, with our present knowledge, is not the case with the 

 two Gemelliporce in question: through the above given characteristics they are very 

 easy to distinguish; but the form of the zooecial apertures, as far as I can see, is to- 

 tally the same, and then, as we have seen in many instances among the Chilostomata 

 to be the case, with a greater richness of specimens, we are forced to wait for a 

 crowding of changes, which will trouble the characteristics. 



Of the typical form, Pourtales, West off Tortugas, has taken some well developed 

 stems, though broken from their origin. They are all of a very uniform thickness and 

 yellowish hue; the stem and branches are about one millimeter thick. The branches turn 

 in all directions, but are all more or less vertical against the stem. In the tip of the 

 branches, the young growing zooecia for the gTeatest part of their length are free, utri- 

 cular. Their wall is perforated by rather large pores. By the proceeding calcification, 

 the pores are closed, and the zooecia are covered by a continuous layer, obliterating 

 their limits, and in which at last their apertures are pierced in the common plane of 

 the surface of the stem. For a good time, however, the distal part of the zooecion 

 with its aperture is raised above this level. The margin of the zooecial aperture, in 

 its distal half, usually bears five spines {setoe). The greatest breadth of the aperture, 



