112 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



This is in part the Membranipora corbula. group of Waters. The recent species 

 belonging to the genus are as follows : 



Hincksina, (Membranipora) ftustroides Hincks, 1880. 



Ilincksina (Membranipora) pyrula Hincks, 1881. 



Hincksina (Membranipora) maderensis Waters, 1898. 



Ilincksina (Membranipora) sceletos Busk, 1858. 



Ilincksina (Membranipora) minuscula Hincks, 1882. 



Hincksina (Membranipora) defensa Kirkpatrick, 1888. 



Hincksina (Membranipora) corniculifcra Hincks, 1882. 



Hincksina (Membranipora) inarmata Hincks, 1881. 



In this genus opposite spines may be able to unite and form a frontal analogous 

 to that in the Costulidne, but this is not a general phenomenon, as it occurs only in 

 very rare zooecia. 



The species of Ilincksina which we have distinguished may be separated into 

 two groups. Those of the first section have small spines and avicularia little dif- 

 ferentiated, while those of the second section are more typical. 



DIVISION I. AVICULARIA LITTLE DIFFERENTIATED. 

 HINCKSINA REPTANS, new species. 



Plate 22, figs. 1-3. 



Description. The zoarium incrusts small pebbles and bryozoa. The zooecia 

 are elongated, elliptical, distinct; the mural rim is thin, salient, rounded, almost 

 equal throughout, bearing with some irregularity from six to eight lateral and two 

 distal spines. The opesium is large, entire, elliptical or irregular. The ovicells 

 are very small and are manifested only as small distal convexities. 



Ao=0.30-0.32 mm. . \Ls=OA5-0.50 mm 



Aooppin ' 



Measurements. Opesia ^.w*.^.. 



70=0.20-0.22 mm. [fo=0.27-0.30 mm. 



Variations. On all of our specimens the lateral spines are very imperfectly pre- 

 served, but the two distal spines are more constant. The mural rim is generally 

 thin, but it may become a little broader (fig. 2). The gymnocyst is much reduced 

 and generally absent. The primoserial zooecia are often modified avicularian 

 zooecia little differentiated. Regenerated zooecia are rare. 



Affinities. This species differs from Hincksina jacksonica in its incrusting 

 zoarium and its more visible spines. 



It differs from Hincksina smithi in its mural rim, which is never enlarged at the 

 base, in its larger micrometric dimensions, its smaller ovicell and in its more in- 

 constant spines. 



It differs from Hincksina vicksburgica in the absence of all proximal crenula- 

 tion of the opesium. 



Among the recent species it has the greatest affinity with Mcmbranipora 

 pyrula as figured by Hincks 1 in 1881, but the ovicells are totally different. 



'Annals and Magazine Natural History, ser. 5, vol. 8, 1881, p. 51. 



