If08] Robertson. — Incrusting Bryozoa. 309 



as'e. Three or four small avicularia scattered over the surface of 

 each zoH'ciiuii, mandible directed transversely or downward. At 

 irregular intervals a lar^e spatuJafe avicularium, sp. av., above 

 or to one side of the orifice, mandible narrowed, curved toward 

 the extremity, and directed obliquely upward. Ooecia globose, 

 punctured with a few large pores. 



A noticeable feature of this species is the position of the spat- 

 ulate avicularia which seem by their large size to push the orifice 

 to one side, thus giving it an asymmetrical position (fig. 80, as. 

 or.). Zocecia upon which these large avicularia develop can be 

 recognized at an early stage, where the orifice is asymmetrical 

 before the avicularium is formed. 



Mucronella calif or nica is found at several localities on the 

 coast of southern California, and was dredged ofif the island of 

 Santa Catalina. 



Retepora Imperato. 



Eetepora Imperato, 1572. 

 Millepora (part) Linnanis, 1766-1768. 

 MiUepora, Pallas, 1766. 

 Millepora, Ellis, 1767. 

 Eetepora, Johnston, 1847. 

 Eetepora, Lamarck, 18.56. 

 Eetepora, Hincks, 1880. 



Zoarium adherent by means of an incrusting base, composed 

 in great part of aborted zooecia. Zooecia disposed on the front 

 surface of an erect, ramose zoarium, Mdiose branches usually 

 anastomose and form a reticulate expansion ; orifice semicircular 

 and semi-elliptical, with a prominent rostrum on the lower mar- 

 gin bearing an avicularium. Avicularia developed on both the 

 dorsal and ventral surfaces of the zoarium. 



This genus, according to Hincks ('80), was founded upon the 

 reticulated habit of growth, but since Retepor£e, according to the 

 same writer, occur in which there is no trace of reticulation, too 

 much weight can not be assigned to this peculiar habit. The 

 species of Retepora found on this coast, however, assume the 

 reticulate form only (pi. 24, fig. 81). The openings formed by 

 the ana.stomosing branches are known technically as feiiestrce, 

 f( II.. and the sides of the fenestra^ are known as trabucula;, trab. 



