392 On a neio Species of Silurian Corals. 



neiglibourhoocl that we may at present place the last-named 

 genus. 



Lastly, Prasopora resembles HelioUtes and its allies in the 

 fact that the corallites are smTOunded by numerous trans- 

 versely tabulate ccBnenchymal tubules ; but the total absence 

 of septa and the peculiar structure of the corallites funda- 

 mentally separate the former from any member of the Helio- 

 poridse. 



Prasopora Grayw^ Nich. & Eth., jun. 



Spec. char. Corallum forming small hemispheric or con- 

 cavo-convex masses, from half an inch to three quarters of an 

 inch in diameter, and from a quarter to half an inch in height. 

 Corallites more or less pi'ismatic, from five to six in the space 

 of one line (counting-in the intervening coenenchymal tubules 

 as well), thus averaging about y^^y to-g-^ij of an inch in diameter. 

 Coenenchymal tubules exceedingly variable in size and form, 

 but rarely equal to half the diameter of the corallites. Epi- 

 theca and internal structure as described in the generic 

 characters. 



Ohs. For an introduction to this unique and very interesting 

 coral we are indebted to Mrs. Robert Gray, Edinburgh. We 

 would take this opportunity of calling attention to the grand 

 series of fossils comprising Mrs. Gray's collection, which she 

 has made from the Silurian rocks of the Girvan district, and 

 to which access has always been given us in the most obliging 

 manner. To the kindness of Dr. Traquair we owe the oppor- 

 tunity of examining a fine specimen of FistuJipora (M'Coy) 

 from the Carboniferous Limestone series of Mid Lothian. 

 This specimen exhibits in a particularly clear manner the 

 characters of that genus, its relation to Prasopora., and the 

 manner in which the two differ, viz. the round or oval coral- 

 lites, separation from one another by an intervening zone of 

 coenenchymal tubuli of considerable extent, and entire absence 

 of the peculiar calicular tabulas which form the exterior zone 

 of each corallite in Prasopora. 



Loc. and Horizon. So far as our present knowledge goes, 

 P. Graym (nobis) is the only known species of our genus 

 Prasopora. It has been obtained by Mrs. R. Gray in mode- 

 rate quantity at Craighead Quarry, near Girvan, Ayrshire, 

 associated with an otherwise abundant fauna, amongst which 

 may be mentioned a small Favosites (apparently the young of 

 F. aspera, D'Orb.). The two are so similar in form as to be 

 easily confounded on a superficial examination. The Craig- 

 head beds are considered by the Geological Survey of Scotland 

 to be of Caradoc age (1-inch map, Scotland, no. 14). 



