^^^^] Robertson. — Incrusting Bryozoa. 269 



rated borxler is always present, and is even found in young 

 zoceeia near the outer growing margin of the colony. This is 

 never true of M. memhranacea of this locality and transition 

 stages have not been observed. The opercula of the two species 

 differ in shape, that of M. serrata being deeper and narrower 

 than that of M. memhranacea. There is considerable resemblance 

 between this species and M. Jnjadesi Jullien ('88). Both have 

 the crenulated border well developed, with the membranous aper- 

 ture, but the spines of our species are not elevated upon a cal- 

 careous tubercle as are those of the Patagonian form. 



Hincks reports this species from Queen Charlotte Islands. It 

 has been obtained in great abundance in Puget Sound, and has 

 been dredged and collected betM^een tide marlcs on the shores of 

 southern California. At Monterey, California, it occurs in free, 

 very much folded and contorted, foliaceous masses. 



46. Membranipora villosa Hincks. 



PI. 16, figs. 22, 22a, 22b, 23; pi. 17, figs. 24a, 24b, 25. 



Memhranipora villosa Hincks, lS80a, vol. 6, p. 84, pi. 10, fig. 8. 

 ?Flustra IsabeUiana d'Orbigny, 1839-1846, vol. 5, pt. 4, p. 18, pi. 

 8, figs. 20-24. 



Zoaria forming somewhat delicate incrustations on the stems, 

 fronds, and floats of kelp. Colonies circular, the lines of zooeeia 

 radiating from the point of origin near the center. By the coal- 

 escence of a large number of colonies the entire surface of frond 

 or float of seaweed is often covered. The first zooeeia formed and 

 those constituting the first few rows near the center of a colony 

 differ markedly in size and ornamentation from those which form 

 the outer rows and larger part of a colony. These latter are most 

 often seen in general collections and are apparently the type de- 

 scribed by Hincks ('80a). The description here given embraces 

 both early and later stages of growth, but for convenience be- 

 cause the later stage of colonial formation is more often met with, 

 it is first described. 



Zooeeia quadrangular, elongated (fig. 22) ; margins thin, with 

 a calcareous, sli<ihtly crenate inner rim; aperture occupying the 

 whole of the front and covered by an exceedingly transparent, 



