12 . MR. A. W. WATERS ON THE MARINE 



nothing to do with the ribs (ridges). I am thus able to confirm part of. what 

 Harmer has written on this point, though it may be somewhat differently 

 stated, and the rows of small radial pores are, as mentioned by Harmer, in 

 line with these spines, and in between are the ribs. We have been accus- 

 tomed to speak as if the ribs were the most important frontal structure, 

 whereas it seems that it is the pores which are the more important, with the 

 ribs produced later and of secondary importance. In specimens of C. Balzaci, 

 and in other species the young zooecia, with only a membranous front, show 

 the pore disks before any calcification takes place, and we may see in many 

 forms that calcification has formed round these pore disks ; and Norman in 

 his figures of C. nitido-punctaia, Smitt, and C. Qattyw, Hindis, shows a 

 thicker calcareous deposit round the disks, though he did not appreciate the 

 importance of his observation. Where there is a distinct area, as in 

 C. Balzaci, &c, and in C.figularis, Hindis, there is a surrounding row of large 

 pore disks, often dark and chitinous, with smaller transparent pores, radiating 

 from the centre, from these large disks. These large pores are probably 

 vestigial, seeming to give a record of ancestors having had spines. The 

 frontal wall of C. radiata occurs right up to the spinous circle, and may be 

 attached to the spines, but this does not justify our assuming that the frontal 

 wall of either C. radiata or other Cribrilince is formed by overarching spines, 

 and it is the supposed resemblance to Membraniporella nitida which has led 

 to this assumption. There are a great many species in various genera in 

 which there is a more or less radial arrangement of the pores, and a fuller 

 study of Cribrilina should explain various structures, for of course the spines 

 and pores show a close developmental connection, even though former 

 explanations may not be correct. 



The opercula measured range in size from C. radiata (form called setosa, 

 Waters) O07-O08 mm.; C. radiata, Cape Verde Islands, O08 mm.; 

 C. Gattyce, 0"07 mm.; C. radiata, some specimens, Ol mm.; C. Balzaci, 

 O'l mm.; C. punctata, Hass., 0"J2 mm. ; C . patagonica, Waters, 0"15 mm. ; 

 C. figularis, Hindis, 0'17 mm. ; C. latimarginala, Busk, 0'2 mm. ; C. mono- 

 ceros, Busk, and C. acanthoceros, MacGr., 0'22 mm. 



C. patagonica, Waters, has on the under surface of the operculum pro- 

 jections of a Membrdnipora type. 



Norman* still considers that there are two species, C. radiata and 

 C. innominata, although most workers have united them, but in my own 

 collection I am unable to find characters by which they can be separated. 

 In British, Naples, and Madeira specimens, which Norman would probably 

 call innominata, there are frequently many avicularia, though some specimens 

 may have few or none. The number of ribs varies from S-20 ; the elevation 

 of the so-called bars is not a satisfactory distinction. 



* '' Polyzoa of Madeira,'' &c., Journ. Linn. Soc, Zool. vol. sxx. (1909) p. 291. 



