HYDllOCORALLINE GENUS ERRIXA. 885 



very rash to propose that they should be separated into distinct 

 species on account of this one character. 



It seems to me, therefore, that the presence of small dactylo- 

 pores in addition to the dactylopores of the oi'dinary type, in 

 other words, the character of dimorphism in the dactylopores, is 

 not a character that should be regarded as absolutely diagnostic 

 either of the genus or of any one of its species. 



As regards the gasteropores there seem to be some variations. 

 In " Benhami " the gasteropores vary considerably in diameter 

 from 0-13-0'17 mm., but in " Ramosa," " Cooki," and " Dendyi" 

 they are more constant in diameter, being 0-27 mm. in the first 

 named, and 0-22 mm. in the latter. It is probable that these 

 figures are not of much value for systematic purposes. Thei'e 

 are many technical difiiculties in the way of making accurate 

 measurements of the mouths of a large number of gasteropores 

 on any single specimen, and unless the average diameter of a 

 large number of gasteropores of one specimen can be compared 

 with similar averages from other specimens of the same facies or 

 species, the figui-es given simply represent a statement of fact 

 concerning a given specimen. The real value of the figures I 

 have given is that they prove that the diameter of the gastero- 

 pores is a variable quantity and cannot be used, except in a very 

 general way, as a guide to the determination of species. One 

 point of rather special interest is that in the facies " Ramosa " 

 with slender terminal branches the gasteropores appear to be 

 actually larger than they are in " Benhami " with thicker terminal 

 branches. This seems to indicate that there is no relation 

 between the thickness of the branches and the size of the gastero- 

 pores, since the expectation would be that the stouter terminal 

 branches would bear the larger gasteropores. 



The presence of a raised margin on one side of the gasteropores 

 in some of the specimens of this species is a feature of some 

 general interest. In some of the gasteropores of the facies 

 " Ramosa" these processes are of considerable size, and bending 

 over the pore have an appearance very similar to the lid of a 

 Gryptolielia. In "Dendyi" they are rudimentary, but in the 

 other specimens they are absent. 



The presence of a definite lip or scale on the edge of the gastero- 

 pore, it must be remembered, was the principal character relied 

 upon by Pourtales for the separation of the genus Lepidopora 

 from the genus Errina, but if we accept Moseley's view that the 

 species of Lepidopora should be incorporated with Eo-rina, then 

 we have a parallel series of variations as regards this character in 

 the Errina group, to that in the Lahiopora group. 



At one time I thought that the difference in the length of the 

 grooved spines (nariform processes) might be a useful character 

 for the separation of the species in this genus. In all the speci- 

 mens, however, I found that the projections on the young actively 

 growing terminal branches are longer than they are on the older 

 branches, and consequently there is a difficulty in fixing a standard 

 Pkoc. Zool. Soc— 1912, No. LIX. 59 



