39 8 Proceedings of the Royal Irish Academy. 



in the Clare Island district. The eye-plates of this form are subject to con- 

 siderable variation. In very young examples the bridge connecting the eye- 

 plates is absent, and its subsequent development into the mature form can be 

 seen in specimens of different growth. In fully grown individuals the eye- 

 plate is distinctly humped on each side of the median incision (PI. I., fig. 6), 

 and in Irish specimens the central muscle-attachment is large and circular. A 

 well-developed chitinous ring is usually present under the hair-bearing pores. 

 The concavity of the hinder margin is generally rounded, as shown in the 

 accompanying figure, or it may be more or less acuminate, as in the typical 

 form figured by Thon (24). The lenses are comparatively large and unstalked. 



In the palps the hump on the third segment is strongly developed, and 

 carries about ten or twelve spines of moderate length, some of which are 

 pectinated. The fourth segment is robust, with six or seven bristles along the 

 inner lower margin ; two or three of these are sometimes pectinated, and there 

 is a row of four strongly pectinated spines along the distal margin of the 

 segment. 



Eylais similis is apparently a common form in Ireland ; and though it 

 seldom figures in local lists, I believe it will prove to be a widely distributed 

 species. 



Eylais celtica Halbt. (Plate I., fig. 4). 

 E. celtica Halbt. (6). 



This is one of the largest species of Eylais ; the type measured about 

 4 mm. in length ; the body is depressed in form, and the epimeral region 

 relatively large. 



The eye-plate is large, being about equal in size to that of large examples 

 of infundibulifera, with a bridge of great length, which is only slightly concave 

 on the hinder margin, and produced in front in a bluntly pointed prominence. 

 There is a small central muscle-attachment connected by a very narrow 

 band of chiton with the eye-plates. The latter are much wider in 

 front than behind — a very unusual character in Eylais ; they are sinuate 

 both on the inner and outer margins, and the front lenses are large and 

 cup-shaped. The hair-bearing pores are placed well within the margins of 

 the plates. 



The capitulum resembles that of E. infundibidifera, especially in the shape 

 of the maxillary plate and pharynx. It measures about "550 mm., not including 

 the posterior side-processes. The latter are short and curved inwards at their 

 apices. The air-tubes reach to a point between the end of the maxillary plate 

 and the chitinous ring near the apex of the pharynx. The latter is long and 

 narrow. The palps are of the infundibulifera- type. Second segment with 



