157 



process. The molar tubercle is neai'ly circular in section and 

 owing to the curving of the basal portion of the mandible is of 

 considerable length, the extremity is square-truncate and is thickly 

 covered with short setas arranged in numerous rows running more 

 or less parallel to one another across the end. Owing to the 

 cutting edge of the mandibles projecting in one direction and the 

 molar tubercle in another it is difficult to make a good drawing 

 of them, to show all the parts and give a good idea of the arrange- 

 ment of them. Figure o of plate xxiii., shows the left mandible as 

 seen fi'om above and a little from within so as to bring the teeth 

 of the cutting edge into view. This part of the mandible projects 

 downwards through the plane of the paper, while the molar 

 tubercle extends obliquely upwards and is somewhat foreshortened 

 in the drawing. 



The right mandible differs from the description already given 

 in having no second or accessory cutting edge — in this respect 

 resembling Asellus aquaticus. The next process crowned with 

 strong seta? is present but appears to have the end narrower so 

 that the setaj are closer together and form two rows, one project- 

 ing on each side ; the molar tubercle has the extremity oblique 

 instead of square-truncate as in the left mandible. 



The mandibular palp is the same in both mandibles. It consists 

 of three joints, the first is short being not much longer than broad, 

 on the outer edge towards the end it bears a number of seta? and 

 on the basal part of the mandible just posterior to the articulation 

 of the palp is a small group of three setae. The second joint of 

 the palp is about twice as long as broad, towards the distal end it 

 bears several rather long setje in groups, some being on the outer 

 margin and others on the under surface. The third joint is about 

 two-thirds as long as the second, it is a little narrowed at the base 

 and narrows also distally. The upper margin is rounded and free 

 from setce, the under surface bears a double row of setaj which 

 gradually increase in length towards the distal end, tiie last two 

 or three being considerably longer than the others and about as 

 long as the joint itself. The sette in one row bear projecting teeth 

 on one side, those in the other appear simple. 



From the description here given it will be seen that the man- 

 dibles are not very different in form from those oi Asellus aquatictis 

 as described by Sars, the chief difference being that the setaj 

 between the cutting edge of the base of the molar tubercle are 

 placed on a raised base so as to form a distinct process, and are 

 moreover somewhat different in character from those found in 

 Asellus. 



The loiver lip (Plate xxiii., fig, 6) consists of two rounded lobes 

 somewhat widely separated distally and connected at the base by 

 a flexible membrane fringed at the margin, and generally seen 

 folded upon itself or puckered when the lip is removed for exam- 



