20 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 7& 



The granulated pleurocyst placed on the median part is always 

 very small, often even it disappears and the frontal appears as a true 

 tremocyst. On the much calcified zooecia the peristome is thickened 

 and festooned in the proximal portion. 



The ovicell appears much smaller when it surmounts a wide zooe- 

 cium. Its diameter measures 0.25-0.30 mm. This is one of the 

 smallest dimensions observed in the genus. The operculum is very 

 thin, semiellipitical, a little elongated without any visible insertion 

 for the opercular muscles. 



Our specimens were living and we have been able to photograph 

 an embryo in its ovicell. 



Affinities. — In the genus Hippomenella there are two rather dis- 

 tinct groups. In the first the peristome is mucronated and the ovicell 

 is richly decorated ; in the second there is no mucron and the ovicell 

 is finely punctate (at least on the young cells). Hippomenella par- 

 vicapitata belongs to the second group, still little rich in species. 

 It is very well characterized by its small dimensions. The ovicells 

 of the other species measure at least 0.35 mm. in diameter. 



Biology. — The species was in reproduction and fixation on April 

 7, 1888. All of our specimens were ovicelled. It incrusts especially 

 the debris of shells ; a single colony incrusted a fragment of echinoid. 



The physiologic function of the small avicularia is not apparent. 

 They do not appear even of any great utility for the greater part of 

 the cells have only one. 



Occurrence. — Galapagos Islands, D. 2813. 



C oty pes.— Cvit. No. 8491, U.S.N.M. 



Genus MICROPORELLA Hincks, 1877 



MICROPORELLA GIBBOSULA, new species 

 Plate 3, Figures 1, 2 



Description. — The zoarium incrusts shells. The zooecia are dis- 

 tinct, separated by a deep furrow, somewhat elongated, irregularly 



hexagonal. The frontal is arched, orna- 



Oy- — ~x mented by small tremopores and fine gran- 

 [^ .J ules. The ascopore is small, median, 



^ B sometimes oblique. The avicularium is 



small, triangular, with pivot, arranged 



^'cROPORE^Arx^S^ ''a, m" transversely in the portion where the cell is 



TRACTABiLis, NEW SPECIES, wldcst and below the ascopore; the beak is 



B, M. GIBBOSULA, NEW • i. T j. 1-1 j. • j1 1M 1 



gpj,(,jj,g oriented toward the exterior; the mandible 



is long, setiform, or, more rarely, lanceolated. 



The apertura is small, semielliptical ; the peristome is little salient and 



bears five spines. The ovicell is globular salient, arranged on the distal 



zooecium, ornamented by pores identical with those of the frontal. 



