VoL. 2] Robertson.—Non-Incrusting Bryozoa. van 
the apertures of the zocecia just above (fig. 24, oe.), their front 
walls perforated by a small number of pores. Rootlets of one 
sort only, extending downward, serving to anchor the colony; 
arising in root chambers just above the lateral avicularia (fig. 25, 
r. ch.) ; the root chambers situated on the lower zocecia only, 
and never appearing unless a root fibre is developed; rounded, 
projecting dorsally and laterally, the root fibre springing from 
the lower side and extending downward keeping close to the 
branch and running parallel with the other root fibres of the 
branch, thus forming a sort of cable or rope for the attachment 
of the colony. 
This species was first described by Dr. John Trask (757), 
but his description was apparently unknown to Hincks (’82), 
who redescribed it under the name of M. compacta. It is per- 
haps the most abundant species of bryozoa on the shores of San 
Francisco Bay and Golden Gate Straits. It grows between tide 
marks on rocks and sea weed forming bushy tufts of a white, 
yellowish or dirty grey color, depending on its age. It is quite 
easily recognized by its excessive spininess. It is found from 
Queen Charlotte Islands to San Diego, but is most abundant 
above Point Concepcion. South of that point it is noticeably 
searce on the shore and in dredgings, and the colonies are small 
and delicate. 
8. Menipea occidentalis catalinensis. Subsp. nov. 
Pl. VII, figs. 26, 27. 
South of Point Concepcion, notably at Santa Catalina and 
San Pedro, M. occidentalis shows considerable variation. The 
internodes more often consist of five or seven zocecia, and 
the seutum which in the type form is a mere spine, or at most 
is slightly flabellate, in the subspecies catalinensis is decidedly 
fan-shaped, the edge being divided and extended into five, six, 
or more spinous processes, making it so large as to cover the 
lower half of the aperture (fig. 26, sc.). One or both of the 
spines that meet over the upper part of the aperture may be 
bifid (c. sp.). The bifid spines and the large and much divided 
scutum are very noticeable features and constitute the chief 
