l'*08] Robertson. — Incrusting Bryozoa. 263 



line made by tlie lower rim of the encroaching wall has the ap- 

 pearance of a rib across the front of the ocecium for which it was 

 previously taken. This species resembles M. unicornis in several 

 particulars, and was formerly so identified. Doubt was always 

 felt, however, concerning the former identification, since the num- 

 ber and position of the spines, the size of the avicularia, and the 

 direction in which the mandible points were different from that 

 given for M. unicornis from other localities. These differences 

 were considered of minor importance since they occurred in ele- 

 ments of the colony which are extremely variable. Now, how- 

 ever, taken in connection with the hooded ovicell they necessitate 

 the formation of a new species. 



Memhranipora occultata has been found at Yakutat and 

 Juneau, Alaska, in both cases incrusting a tunicate. 



40. Memhranipora patula Hincks. 



PI. 15, fig. 10. 



Memhranipora patula Hincks, 1881, vol. 7, p. 150, pi. 9, fig. 4. 

 Memhranipora patula Hincks, 1882, vol. 10, p. 465. 



Zoaria forming brown or reddish brown patches on rock, 

 pebbles etc. Zooecia large, short and broad, distal extremity 

 much raised; aperture occupying from two-thirds to three-fourths 

 of the front wall, usuallj^ broader than long, arched above, low^er 

 rim curving outwardly ; the lower portion of the front of the 

 zooecium covered by a delicate calcareous lamina which is often 

 continued up the side and around the top of the aperture (pi. 15, 

 fig. 10). Four, five, and sometimes six long, cylindrical, jointed 

 spines on the upper margin, S2^. From the back of the zooecium 

 and arising some distance below the distal margin, an avicular- 

 ium, av., which viewed from the top is triangular in shape with 

 mandible directed distally, or toward the growing rim of the 

 colony; frequently absent. Oo^cia. uc., shallow, smooth, scattered, 

 apparently immersed in a forest of spines. 



Memhranipora jyatula is reported by Hincks from California, 

 and in large quantity and of luxuriant growth from Queen Char- 

 lotte I.slands. Small colonies have been obtained at several south- 

 ern localities at depths varying from 15 to 42 fathoms. 



