2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 9I 



friable. The surface is even, with no detachable ectosome, but at the 

 surface tangent spicules (or clads of spicules) make a tangent net- 

 work. The numerous conspicuous oscules average about i mm in di- 

 ameter and occur about 7 to the square centimeter. The internal struc- 

 ture is rather confused, with large spicules optically evident. The 

 megascleres comprise calthrops, with rays each about 50^1 by 625 /x, 

 and oxeas 60 /x by 3,500 jx. The microscleres consist of streptasters or 

 spirasters with scarcely any spiral to the main shaft whatever, and 

 with a great many long spines, so that the total mass has a diameter 

 of 10 fx as compared to a length of only 15 /a. The spirasters bear 

 resemblance to caterpillars. There are also metasters, with only 6 

 to 12 rays each, the outside dimensions of the entire spicule being 

 about 40 ft to 50 /t, Microrhabds 3 /t by 155 ;«. are rather common. 

 Furthermore, occasional reduction-derivatives of the metasters are 

 present, having only 2 or 3 rays. 



Interesting comparisons may be drawn between this species and 

 Pachastrella inonilifera Schmidt (1868, p. 15), a cosmopolitan spe- 

 cies that has been recorded from the West Indies. It is conceivable 

 that the present specimen represents an uncommon malformation 

 of inonilifera, though there are sufficient points of difference to ren- 

 der such a hypothesis improbable. P. inonilifera does not have the 

 long raphides, but instead centrotylote microrhabds only lo/x to 20 /a 

 long. Instead of the large metasters and the peculiar caterpillarlike 

 spirasters, it has rather commonplace small spirasters about 14 fi 

 long. P. cribrum Lebwohl (1914, p. 78), from Japan, may possibly 

 be related here. Its larger metasters are smaller than those of dilifera, 

 the smaller spirasters much shorter and with fewer spines, and the 

 microrhabds twice as thick without being longer. 



Family CORTICIDAE Vosmaer 

 ROOSA, XI. gen. 



This genus is proposed for the one new species described below, 

 having as spicules diacts with peculiar medial distortions. The oc- 

 currence of a few rare triacts and angular diacts confirms the hy- 

 pothesis that the spicules are probably reduced calthrops. 



Genotype. — Roosa zyggonipha, new species. 



ROOSA ZYGGOMPHA, n, sp. 



Holotype. — U.S.N.M. no. 22277; ^^0"'' station 17, latitude 

 i8°3o'oo"N„ longitude 66°io'3o" W. to longitude 66°i2'2o"W,, 



