436 SYSTEMATIC PALEONTOLOGY 



the new genus lie. Jlydmciinia is farther removed, though doubtless 

 also related. Again, 1 think it possible that some relationship to the 

 PoRiTiD^ may be detected when fuller comparisons than are now possible 

 can be made. 



MiLLEASTER INCRUSTANS n. Sp. 



riatc CXXI, Fig. 10. 



Description. — Polyparium encrusting, growing on shells of gastro- 

 poda, over which it forms thin, rough, scabrous expansions, 1 mm. or 

 less in thickness, that may be separated cleanly from the invested host, 

 the shell showing no trace of being absorbed by the coral. Surface ex- 

 hibiting irregularly distributed, elevated and thick-lipped pores, the 

 mouths of which are distinctly, though often rather irregularly, stellate. 

 Pseudo-septa strong, usually six in number, but varying from four to 

 seven, usually leaving but a narrow space between them to form the rays 

 of the stellate orifice, and sometimes even joining laterally so that 

 nothing but a minute central opening remains. Greatest diameter of 

 elevated rim enclosing this set of zooidal pores averaging about 0.25 

 mm. ; where closest and most regularly disposed about four occur in 

 2.0 mm,, but not infrequently the depressed interspaces may attain a 

 width of fully 1.0 mm. In tliese interspaces usually somewhat larger 

 and fewer openings occur. These arc irregularly rounded and not 

 septate like the elevated pores, thougli their apertures may appear to be 

 irregularly stellate because of the astrorhizal grooves which (Mupty into 

 them. The latter, though always present, are never conspicuous, and 

 where the elevated pores are al)undantly developed may even be over- 

 looked. The small rounded openings of a third set of pores are scat- 

 tered among the granular surface terminations of the coenenchymal 

 tissue. The surface granules of the latter are usually separate, but may 

 be confluent. 



This hydrozoan is associated with Ilydractinia muUispinosa and like it 

 apparently always grows on shells of gastropoda. But, so far as ob- 

 served, it never absorbs the shell of its host. Aside from being much 

 less common — indeed, it must be counted among the rare fossils — its 

 peculiarities are so striking and distinctive that it should be recognized 

 at once when found. 



