ACTINOPOBA. 173 



Diagnosis. Cyclostomata Tubulata in which the zooecia are 

 simple, short, open tubes. They pass through a Defrancia stage 

 (? always). The zooecia are monomorphic. The apertures occur 

 along raised ridges. 



Affinities. This family is here accepted for a series of forms 

 which have the apertures occurring along raised ridges, instead of 

 in disconnected tufts, as in the Fascigeridae. The character of the 

 young zocecia (as in B. 2295) shows that the zoarium of Theonoa 

 begins with typical, Tubulate zocecia; while D'Orbigny's 1 figure 

 of a member of this group shows that it passes through an Apsen- 

 desia stage. The simplest form of the zoarium is a flat, adnate disc, 

 which agrees with Lichenopora, except for the absence of cancelli : 

 that this form arises from a Defrancia larva cannot be proved ; but 

 Haime's figure of Actinopora phillipsi, with its central depression 

 and its radiating ridges, presents such a striking resemblance to 

 the Pelagia or Defrancia stage of Apsendesia cristata, Lamx., that 

 this is highly probable. To produce Actinopora from "Pelagia 

 clypeata" we have only to thicken the epitheca so as to give the 

 zoarium an attached habit, and then allow of the formation of 

 the peripheral selvage by further growth. 



In the Theonoidae as here defined, Actinopora is the primitive 

 form. The first advance from this is a compound zoarium of many 

 Actinoporoid discs growing into an encrusting sheet. This is the 

 genus Kololophos. By a further development, erect, frondose 

 zoaria are produced the genus Theonoa. Growth into masses 

 forms the genus Multitubigera. 



ACTINOPORA, D'Orbigny, 1852. 

 [Pal. franQ. Terr. cret. t. v. p. 762.] 



SYNONYMY : 



Lichenopora, Haime, non Defrance. 

 Defrancia, pars, Hagenow, non Bronn. 

 Tubulipora, pars, M. Edwards. 



Diagnosis. Theonoidse in which the zoarium is a flat, simple, 

 adnate disc. The zoarium consists of a central depression ; a rim 

 crossed by radiating ridges ; and usually a flat, peripheral selvage. 



1 D'Orbigny. Pal. fran9. Terr. cret. t. v. pi. Dcclxiii. figs. 10-12. 



