Halbkkt — 77/6 A carina of the Seashore. 121 



marked, and cany a long bristle. Second .sliield nearly as bn^ad as Llie first, 

 strongly narrowed lo the end margin, wliieli is straight, with a pair of long 

 bristles, and on the inner side of these a pair of very short hairs. The hair 

 armature of the dorsal surface is much as in the protonyniph. Anal plate 

 small, placed at end of body, and carrying two pairs of long hairs, and a 

 terminal spine. This is tiie nympha coleoptrafa form. 



Habitat. — A species of the lower intertidal area, occurring between 

 limestone flakes and in crevices in the Vesiculosus and Serratus zones at 

 Malahide. At Ardfry it was also found in these zones under boulders partly 

 embedded in sandy mud and in moist places. Adults and nymphal forms 

 were observed both in the summer and autumn months. 



Hydrogamasus Giardi (Berl. et Trouess.). (Pi. XXI, fig. 4.) 



1889 Seius Giardi Berlese et Trouessart 20. 1889 Gammus Giardi 

 Moniez 38, p. 193. 1892 Hiidrogamasus Giardi Berlese 3, p. 72. 1915 

 Halbert 25, p. 65. 



This species is found ou a wider range of the shore than the preceding, 

 occurring freely from the Pelvetia down to the Serratus zones on the rocky 

 shore at Malahide, usually in crevices and between tiakes in from moist to 

 wet places. At Ardfry it occurred in the corresponding zones under 

 boulders resting on sandy mud. The sexes are almost equally abundant, 

 and the dates of capture range from April to October. 



Frequently found in company with H. littoralis ou the lower part of the 

 shore. The two species are structurally very much alike, but they may be 

 separated by the following characters : — 



HydrofjaviasHS littoralis, larger ; length of female, about 940/u ; breadth, 

 560/^ ; length of male, 922ju ; colour paler ; form more oval ; hairs of dorsum 

 relatively longer. Fissure separating dorsum from anal shield reaching the 

 end margin of body. 



Hyd^rofjamasus Giardi, smaller; length of female, 640^; breadth, ."12/u • 

 length of male, 563/i ; colour much darker ; body hairs shorter. Fissure not 

 reaching end margin of body. 



The supposed difference in the fusion or otherwise of the anal and dorsal 

 plates in these two species does not occur (3). As a matter of fact, these 

 plates are fused at their end margins in both species. A figure of the male 

 chelicerae of H. Giardi is given (PI. 1, tig. 4) ; those of //. littoralia are very 

 similar. 



Two other species of Hydrogamasus ha\e been described, i.e., II. Silvcstrii 

 Berlese (6), from the Italian coast (Portici), and II. antarcticv.-t, Trag., from 

 Paulet Island. 



R.I. A. PROC, VOL. XXXV, SECT. B, \R\ 



