1908] Robertson. — Incrusting Bryozoa. 267 



a single broad calcareous plate. In this stage the margin of the 

 aperture becomes thicker and acquires from four to six short 

 spines directed inward. 



The various stages of growth of this species are thus seen to 

 be extremely diverse and w^ell marked. Whether or not the vari- 

 ous synonymes refer to the same species is difficult to say without 

 a knowledge of these stages of growth. D'Orbigny ('39- '46) 

 first described M. tehuelcha from Patagonia and reports it as 

 abundant on the east coast of South America from Pernambuco 

 southward. Waters ( '98) suggests that 31. liyadesi Jullien, from 

 Cape Horn, may be the same thing or a variety. This may be so, 

 although the size and the relatively slight amount of calcareous 

 deposit would seem to separate M. liyadesi from M. tehuelcha un- 

 less Jullien has figured an immature specimen. M. hyadesi is, 

 perhaps, more closely related, as I will show, to M. serrata Hincks 

 of the California coast. The present species seem to be closely 

 related to, if not identical with, Amphihlustrum bitubercidatum 

 Ortmann, both having the blunt, calcareous tubercles and the 

 aperture much reduced by the growth of the calcareous deposit 

 around it. 



Membranipora tehuelcha is obtained from San Francisco 

 southward on our coast. It is one of the most abundant species 

 on the rock-weed at La Jolla, San Diego, and San Pedro. 



44. Membranipora membranacea (Linnaus) Blainville. 



PI. IG, figs. 19, 19a, 20. 



Flustra membranacea LiniiEeus, 1766-68, p. 1301. 



Flustra membranacea, Ellis and Solander, 1786, p. 18. 



Memhranipora membranacea, Blainville, 1834, p. 447. 



Flustra membranacea, Johnston, 1847, ed. 2, p. 348, pi. 66, figs. 1, 



2, 3. 

 Eeptoflustra telacea, d'Orbigny, 1850-52, p. 324. 

 Membranipora membranacea, Busk, 1854, pt. 2, p. 56, pi. 1. 

 Membranipora membranacea, Hincks, 1880, p. 140, pi. 18, figs. 5, 



6; pi. 68, fig. 2. 



Zoaria consisting of circular patches from two to five or six 

 centimeters in diameter incrusting stems and fronds of fucus. 

 ZooBcia quadrangular, oblong, alternate (pi. 16, fig. 19) arranged 

 in lines radiating from a center (fig. 20) ; margins slightly raised; 



