270 University of California Publications in Zoology. [Vol. 4 



membranous front wall; operculum, when closed, apparently of 

 the membranaceous type, i.e., consisting of a semi-circular chitin- 

 ous rod (fig. 22a) ; when partly open (fig. 22b) the rod is seen 

 to be widened at the proximal extremities affording a wide base 

 for the attachment of the opercular muscles, mus. att. Spines 

 are of three kinds on each zooecium : a stiff, curved, flaring spine 

 (fig. 22, fl. sp.) at each upper or distal angle; on the lateral mar- 

 gins, at irregular intervals, one, two, or more flat spines, lot. sp., 

 flaring outward ; springing from the wall of the aperture, extend- 

 ing from the lower end of the operculum around the zooecium, a 

 short distance within the crenate margin, a row of 15 or 20 min- 

 ute frontal spines, fr. sp., whose points are directed toward the 

 median line. Occasionally, at the middle of the upper margin 

 of some zooecia, a tall hollow spine, t. sp. These tall processes 

 are probably of a different nature from the ordinary bryozoan 

 spine. They usually occur at a point where two lines of zooecia 

 either converge or diverge, and are most abundant on colonies 

 spreading over an uneven surface. At the points where zooecia 

 converge, e.g., triangular or circular spaces are frequently formed 

 within some of which a polypide may sometimes be found, and at 

 the angles or irregularly around the margin of such spaces extra 

 large spines frequently occur ; at other times, instead of a zooe- 

 cium, a tall spine-like process develops, t. sp., this process being 

 probably homologous with the zooecium and contained polypide 

 which should otherwise have developed at that point of the col- 

 ony. 



A young colony consisting of only seven zooecia is shown in 

 fig. 23. The zooeda are oval in the earliest stage, becoming some- 

 what elongated in the second and third rows; margin thin, 

 rounded above, raised, without the crenate, calcareous, inner 

 rim; aperture occupying the whole of the front, covered by an 

 exceedingly delicate membranous front wall; margin surrounded 

 by spines of great length which are frequently much branched, 

 hr. sp. On the third zooecium, c., minute frontal spines occur on 

 the membranous front wall at more or less regular intervals in- 

 side the margin, and these structures are found on all future 

 zooecia of the colony, while the branched marginal spines dis- 

 appear. 



