1908] Robertson. — Incrusting Bryozoa. 261 



the iiiiinber and size of the aviciilaria, occurs in the specimens 

 from different localities, as also in various portions of the same 

 colony. The number of spines as given in the diagnosis and as 

 shown in fig. 3 is found only in the younger zooecia, or upon those 

 in ])rotected positions and without ovicells. The delicate spines 

 on the lower half of the zocpcium are exceedingly variable, four 

 being the commonest number, though sometimes there are only 

 three, and again there may be six. But few of the large avicul- 

 aria (fig. 4)j which are merely transformed zooecia, have been 

 found and those on colonies from northern California. 



Comparison of the various specimens in this collection with 

 M. Jiorrida Ilincks, and 31. calif orniensis Waters, leads me to 

 suspect that these are one and the same species and identical with 

 the form here described. Certainly the resemblances between 

 ooecia and avicularia are striking and most of the differences can 

 be accounted for either by imperfect description due to a lack of 

 material or to variation due to differences in environment. 



Memhranipora Jiorrida is reported by Hincks from California. 

 It is present in our collection from Puget Sound, Washington ; 

 also from various localities on the northern coast of California, 

 Pacific Grove being the most southern point from which it has 

 been obtained. M. californiensis is reported by Waters from 

 California. 



38. Membranipora lacroixi (Audouin) Hincks. 



PI. 14, fig. 5. 



Flustra Lacroixii (Audouin) Savigiiy, 1811, pi. 10, fig. 9. 



Flnstra clistans Hassall, 1841, vol. 7, p. 369. 



Membranipora Lacroixii, Busk, 1854, pt. 2, p. 60, pi. 69, figs. 1, 2, 



3, 4, 5. 

 Bifustra Lacroixii, Sniitt, 1873, pt. 2, p. 18, pi. 4, figs. 85-88. 

 Membranipora Lacroixii, Hincks, 1880, p. 129, pi. 17, figs. 5-8. 

 Membranipora Lacroixii, Waters, 1898, p. 679, pi. 48, figs. 14, 15. 

 Membranipora Lacroixii, Kobertson, 1900, p. 323. 



Zonrium forming a dark reticulated incrustation over shells 

 or other bryozoa. Zoa'cia oval, somewhat elongated, aperture 

 occupying the whole of the front; margin thickened, rounded, 

 granulated, sometimes forming a prominent ridge, sometimes 



