824 Proceedings of the Royal Irish Academy. 



This form appears, on the whole, to approach very closely to 

 T. coronatum, Hub. ; but in the frequent possession of opaque 

 white fields and lines, it presents characters claimed exclusively 

 by Burger for T. diadema and T. ylanduUferum. It must be 

 obvious, however, from the above details, that the relative 

 development of conspicuous patches and lines of gland-cells, 

 like the exact disposition of cephalic pigment, is a matter of far 

 too inconstant a nature to be of specific value. Yet these 

 characters have been largely relied on by Biirger, and others, in 

 the useless multiplication of species. 



Among the specimens of T. coronatum at Naples, Burger has 

 observed sexual dimorjjhism. Females are about twice as long 

 as males, and of a different colour. I have not found this to 

 be the case at Valencia. Examples of both sexes were noted, 

 with well-developed genital organs, measuring less than 1 cm., 

 and as much as 3 cms. in length. 



On the Coralline ground in the Port Magee Channel, a 

 number of specimens were dredged quite distinct from the 

 above. These measured from 5 mm. to 12 mm. in length, and 

 were relatively stout and round in figure. The head wide, 

 rounded, and fairly well-marked off. Eyes, large. In colour they 

 were a very deep rich yellow (approaching the colour of fig. 1 6, 

 pi. iii., in the JSTaples Monograph), depending largely on the pre- 

 sence of yellow and orange granules in the skin, the gut beneath 

 being also yellow. A patch of dark brown pigment of oblong 

 or oval shape, concealed the anterior eyes within its straight or 

 convex anterior margin, while posteriorly the pigment was 

 scantier, so that the hinder margin was ill-defined. Males and 

 females were present in about equal numbers; individuals of 

 both sexes, even of the smallest size, having well-developed 

 gonads. 



It is probable that this, and the short thick deep-yellow 

 form from the same locality, described under T. candidum, are 

 the same species, the pigment band on the head not being a 

 constant character. Individuals intermediate with respect to 

 this point have been already mentioned (p. 822). 



Tetrastemma vermiculatum (de Quatr.). 



Common, and generally distributed in Valencia Harbour on 

 the shore and dredging grounds, but hardly so abundant as 

 T. fnelanocephalum. There seems little to distinguish this 



