A REVISION OP THE GENUS STEGANOPORELLA. 277 



with A-shaped sclerite in the b opercula. The union of the 

 cryptocyst with the distal wall, and the deep cavity of the 

 median process, are also important characters. 



MacGillivray states that this form is Escharau, Hemes- 

 charan, or encrusting. He records an Escharan colony which 

 measured no less than 13 X x 6 inches. Of the material 

 at my disposal, c and d are mere fragments, a and h are both 

 bilaminar or Escharan, with anastomosing plates, and have 

 somewhat the habit of Lepralia foliacea. At the lines of 

 union of the plates the two layers of zocecia divei'ge, so that 

 hollow cavities originate, lined by the basal walls of the 

 zooecia. Considerable unilaminar pieces may thus occur at 

 the nodal lines. The ratio of a to b is about 4 — 5 : 1. No 

 constant difference in this ratio was noticed in "different 

 parts of the colony, or on its opposite faces. 



The edge is thin, a good deal raised, and well separated 

 from the post-oral shelf. This is slightly tubercular, deep, 

 and massive, being well developed even proximally. The 

 oral shelf is about equally developed in a and b. It has the 

 form of a perfectly smooth rounded fillet, a well-developed 

 concave space with smooth floor occurring between it and 

 the oral arch. The condyles are strong, especially in b. 

 The oral arch is slightly raised; that of b semicircular, of 

 A with straight parallel sides and a truncate distal border, 

 which is usually slightly concave distally. Cryptocyst either 

 sloping gently into the post-oral shelf or sharply separated 

 from it; its horizontal portion is very small, thick, and with 

 small pores, whose outer opening may be obviously smaller 

 than the inner opening. It slopes steeply, but without any 

 angulation, into the cavity of the median process. The 

 cryptocyst is usually porous in this region, but an imperfo- 

 rate part, forming the proximal wall of the cavity, may be 

 separated fcom the horizontal part of the cryptocyst by a 

 curved line, as in S. buskii. The median process has a deep 

 cavity, floored by the convex roof of the tube, which may 

 arise from the cryptocyst at an angle (as in fig. 9), or with 

 a continuous slope. The borders of the median process are 



