Young — On the Genus Heterophyllia. 449 



6th. There are six septa, which are 6th. There are six septa, which are 



united by a linear septal columella. united by a linear septal columella. 



7th. The endotheca is tolerably 7th. The endotheca is scanty, and 



abundant. the dissepiments are wide apart. 



8th. The diameter of the corallum is 8th. The diameter of the corallum is 



1-1 0th inch or less. rather more than l-20th inch. 



9th. In the Carboniferous limestone of 9th. From the Carboniferous limestone 



Craigenglen, Stirling, and Brockley, of Craigenglen and Brockley. 

 Lesmahagow, Lanarkshire. 



From the above descriptions it will be seen that the two species, as 

 described by Dr. Duncan, have many characters in common, and I 

 am satisfied that, had he examined a larger number of specimens, he 

 would have found every variety connecting them. 



In the first place this coral has never, so far as I am aware, been 

 found with its extremities perfect, fragments occur from three to 

 four inches in length, but generally it is found in shorter pieces ; 

 these are of every diameter between -j-V and ^-o i^^h or less. One 

 specimen, 3 J inches in length, tapers in that distance from -j-V to -qV 

 inch in diameter, showing that measurements from fragments of 

 various sizes are of no specific value. 



All the larger specimens are more or less flexuous, some of them 

 being much curved, and occasionally bent at right angles ; this is the 

 case with both stout and slender specimens of the corallum. 



The curved hook-shaped processes which are described as one of 

 the principal specific characters of S. mirahilis, I consider as of no 

 value in distinguishing that species, for we possess specimens of 

 every diameter as formerly quoted, showing these little booklets. 

 On nearly every specimen which is found embedded in the shale 

 they may be exposed with careful manipulation. Indeed it seems to 

 have been the perfect condition of the corallum, large or small. In 

 weathered specimens of the stems, found lying upon the shale-banks, 

 the booklets are always broken off, but their bases may still be traced 

 upon the costse, or in the grooves to which' they were fixed. 



Dr. Duncan states that H. Lyelli is only occasionally tuberculated, 

 but the specimen of this species which he figures in pi. xxxi., fig. 

 4, c, is as regularly tuberculated as that shown in his figures of 

 jff. mirahilis. Except in very much worn specimens, the tubercles are 

 always present upon both large and small diameters of the corallum, 

 and as they are sometimes seen to vary slightly in number and 

 regularity, even upon parts of the same stem, mere irregularity of 

 occurrence is not, therefore, to be considered of any specific value. 



The costge and intercostal spaces are also characters that vary 

 considerably in this coral, and cannot, I think, be depended upon as 

 points of specific distinction, as some specimens of the largest 

 diameter have costse less developed than those seen upon more mode- 

 rately-sized stems. The intercostal spaces are wide, shallow, or 

 deep, according to the diameter of the specimen, and the prominence 

 of the costae. 



In H. Lyelli, the horizontal section of the corallum is stated to be 

 hexagonal, in H. mirahilis, mostly circular ; this is a point that 

 appears to me of no value in the diagnosis of the species, as the 



