ART. 14 



FOSSIL AND EECENT BEYOZOA CAN^U AND BASSLER 



79 



The radicells form a true passageway between the colonies and the 

 algal substratum; they are fragile, hollow, terminated in a brush. 



The mandibles are very thin and transparent. The zoarium is 

 unilamellar, very often cylindrical, for it encrusts algae. It may also 

 creep over nullipores (Smitt). 



Biology. — The color in life is a bright vermillion (Osburn). The 

 calcareous skeleton is much less pigmented than the ectocyst. The 

 operculm is light colored. The giant species have not much vitality. 



Fig. 12.— Genus Petrauella, new genus. A-I. Petrauella bisinuata Smitt, 1873. 

 A. Operculum, X 85, with broad, chitinized marginal band. B. Another oper- 

 culum, X 85, with narrow marginal band. C. Another form of operculum, X 85. 

 jD. Operculum, X 85, in which the proximal articulation with the compensatrix 

 IS visible. E, F, O. Three mandibles, X 85. H. Radicel of this species, X 85. / 

 Petrauella marginata, new species. Operculum, X 85, with narrow marginal band 



For example, on the same alga a larva of Cellepora was fixed near a 

 Petraliella larva; the two colonies are well developed at first, but the 

 Cellepora stopped the Petraliella and became superposed upon it. 

 Likewise in the interior of a tube of Petraliella a larva of Smittina 

 trispinosa was afiixed; it developed normally in pursuing completely 

 the radicular system which did not disturb it at all. When they are 

 useless by death or putrefaction of the substratum, the radicells dis- 

 appear; also the interior face serves as "a refuge for small parasitic 

 species such as Hippothoa, which find here an excellent refuge to shel- 

 ter their extreme fragility. We have made the same observations on 

 Petraliella vorax, new species, of the Philippines, where we were able 

 to determine the same parasites. 



