262 Prof. J. C. Schlodtc on the 



berance fits into a socket in the pleural margin of the head , 

 they have an oscillating* movement, determined by this 

 protuberance as a pivot and by the outer margin of the stipes. 

 Those special arrangements for regulating the movements 

 which will be described in the two other principal types are 

 here wanting ; and this series of Amjjhipoda might therefore 

 suitably be described as Elciitherognatha. 



In illustration of the combination which prevails among 

 most of the Gammariis-CapreUa type, we may take before us 

 the structure of the mouth in Caprella septentrionalis^ Kr. 

 Looking at the head from the side, after having taken away the 

 maxilliped with its strongly developed lobes and palpus armed 

 with claws, we note first the flat and broad clypeus and upper 

 lip ; next, the epipharynx or palate, which forms a flatly 

 rounded part in front of the opening of the pharynx ; and 

 finally, a portion of the lower lip, which appears between the 

 mandible and the first pair of maxilla3, and which deserves 



f)articular attention as it plays a very important, hitherto over- 

 ooked, part in the mechanism of the mouth. A fuller view 

 of it is obtained by examining the head from below, after 

 removing all the appendages of the mouth except the mandi- 

 bles, so that the hypostoma appears with the sockets in wdiich 

 the two pairs of maxillte articulate ; in front of these we tlien 

 observe the same portions of the lower lip which we saw from 

 the side, forming on each side a short horn, pointing back- 

 wards, and placed close under the stipes of the mandible, 

 whilst the remainder of the lower lip, which is considerably 

 developed, forms four cushion-like lobes round the orifice of 

 the mouth. Two, of more oblong shape, are placed in front 

 and extend laterally, whilst the two others, of obovate outline, 

 are placed in the middle ; but the bases of all point towards the 

 mouth. The two foremost of these cushions fit very closely 

 behind the mandibles ; all four have a much smaller quantity 

 of chitine and lime in their composition than the two horns of 

 the lower lip above described ; these therefore are stiffer than 

 the cushions, yet yielding towards their outer extremity, and 

 thus constitute a kind of spring, stiff enough to keep the man- 

 dibles up in the proper position for their oscillating movement, 

 yet sufficiently elastic to yield to pressure when the mandibles 

 are moved. We may, therefore, very properly describe these 

 homs as processus mandibularii labii inferioris. The left 

 mandible is somewhat stronger and more elaborately armed 

 than the right one ; both have a powerful and very prominent 

 masticating process on the inner side, with elliptic rough 

 crown, bearing inside the inner corner a single hairy filament. 

 The broad transverse edge of the outer lobe is cleft into five 



