796 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



The vacuoles 1 are the small, oblique, recurved tubules which irregularly 

 perforate the zoarium. They open at the base of the sulci and they are separated 

 by nervi or threadlike ridges which are longitudinal on the dorsal and often 

 oblique on the frontal. The vacuoles apparently are not connected with the 

 cavities of the zooecia. 



The squamous composition of the zoarium seems to indicate an external 

 origin somewhat analogous to the pleurocyst of the Cheilostomata, but the corre- 

 sponding division into two of the ectocyst has not yet been observed, although it 

 may be quite probable. 



Hennig (fig. 256P) thought that the polypidian tubes were inserted on a 

 longitudinal dorsal tube. Our longitudinal sections have not confirmed this obser- 

 vation. The successive ramification of the tubes is identical with that of other 

 families. The removal of the dorsal shows the ordinary lozenge-shaped areas. 



In horizontal section the tubes are perceptibly equal. They do not diminish 

 from the circumference to the center as in the zoarial form Entalophora, therefore 

 they are cylindrical. 



The zoarium is often bushy : the frontal bearing the apertures is turned to 

 the interior of the colony toward the median axis; the dorsal, on the contrary, is 

 exterior. There are some flabelliform zoaria, but very rarely on the same plane. 



The Hornericlae are attached to rocks or algae by an expanded base. 



The larva is the largest of the Cyclostomata. There are only a dozen embryos 

 in the ovicell. 



Genus HORNERA Lamouroux, 1821. 



1821. Uornera LAMOUROUX, Exposition methoclique cles genres de 1'ordre des Polypiers, p. 41. 



The ovicell is large, dorsal ; its punctations or reticulations are large. The 

 tubes are cylindrical with dorsal gemmation. The apertures are disposed only on 

 the frontal. The vacuoles are arranged all over the zoarium at the base of longi- 

 tudinal sulci. There are nine tentacles. 



Genotype. Hornera frondiculata Lamouroux, 1821. 



Range. Lutetian-Recent. 



Hornera is quite well known and is a very natural genus. It is very common 

 among the Tertiary fossils. Certain Cretaceous species have been cited, but we 

 believe that it is necessary to await the description of their ovicells and of their 

 sections before assigning them definitely to this genus. 



The variations in this genus are extraordinary and it is often useless to 

 attempt to determine an isolated specimen. 



Species of Hornera are bryozoans of deep water. All the recent species live 

 at variable but always very great depths. At 30 to 100 meters one may hope to 

 find some examples, but it is at greater depths, from 100 to 300 meters these 

 animals find the most favorable conditions for their development. 



The thermal conditions of their habitat vary evidently with the depth, but 

 in the rather restricted limits from 9 C C. to +6C. 



1 Intermediate pores (D'Orbisny). Interskeletal cavities (Pergens). Branched maculae (Gregory). Ad- 

 ventitious pores (Waters). 



