Ilydractiiiia, Parkeria, and Strom atopora. 65 



Gcncrnl tonn irn\L,ailaiIy sul»<^lnl)ular, bossed with four or 

 more inonticular cininenccs ot" unequal size and hei^^ht, which 

 meet cacli other at their circumference3 rcspeetlvcly. Com- 

 position calcareous. Colour whitish grey. Surface granulated 

 from the wcatiicring of minute reticulation formed by the 

 anastomosing of delicate tissuc-tibrc ; tissue-fibre like a mass 

 of crochet-knitting, the thread of which is about 3-1 SOOths inch 

 in diameter, and the interstices a little more, viz. about 

 5-lSOOths inch in diameter; opaque, whitish on the surface, 

 transparent in the interior, but not coated with granular calcspar 

 as in Parl-eria ; presenting circular apertures about 12-1 SOOths 

 inch in diameter (now filled up with calcareous material), 

 densely scattered at variable distances from each other on the 

 sm-face throughout the tissue-fibre ; also a stellate arrangement 

 of branched grooves which, radiating from the summit of each 

 boss or eminence, finally mingle in their ultimate divisions 

 with those of the surrounding eminences ; but with no appear- 

 ance of aperture on the summit ; crossed by a creeping, 

 branched, tortuous, dendriform fibre in prominent relief, which 

 appears to be independent of the grooves, although in intimate 

 relation with tlia tissue-fibre, which it penetrates or issues from 

 here and there, sometimes dipping under a portion to appear 

 again after a short distance, and sending off laterally minor 

 branches throughout the whole of its course ; largest branches 

 about 10-1800ths inch in diameter, cylindrical, and composed 

 of a thin opaque layer externally, filled witli transparent calc- 

 spar interiorly. Internal structure consisting throughout of 

 the same kind of delicate, anastomosing, tortuous tissue-fibre 

 seen on the surface, traversed by straight circular tubes from 

 5- to 12-1800ths inch in diameter and at variable distances 

 from each other of 5- to 20-1 SOOths inch, which assume a 

 radiating direction as they increase in number with their 

 distance from the centre to the circumference, where the last 

 open on the suifaec by the apertures above mentioned, or did so 

 before they were fossilized and filled with calcspar. Each 

 tube now composed of a white opaque cylinder filled with trans- 

 parent calcspar,- the centre of which is also opaque and clouded. 

 Size of specimen | inch in its greatest diameter ; width of 

 widest grooves, that is, at the summit of the boss, l-24th inch 

 in diameter. 



Hah. Marine. Lower White Chalk. 



Loc. Dover. 



Ohs. I am informed by ]\Ir. H. Brady, who had previously sent 

 me for examination a thin slice of a fossil similar to th.at above 

 mentioned, that Dr. Stache, of Vienna, has described and named 

 it, as above stated, " provisionally." lie obtained his speci- 



Ann.&Mag. N. Uist. Scr. 4. Fo?. xix. 5 



