264 Prof. J. C. Scliioclto on the 



the upper face of the right-hand l)hide,on whicli the prehensile 

 hook is undivided and extremely finely pointed. The fore- 

 most lobes of the fiat lower lip are thin and pointed ; the 

 middle lobes are roundly emarginated in front, leaving a part 

 of the jialate in front of the pharynx uncovered ; the mandi- 

 bular springs, on the contrary, are somewhat dilated and very 

 stifi". If we then proceed, by taking away the upper lip and 

 folding the entire lower lip back from the hyi^ostoma, we ob- 

 serve the grinding-tecth of the mandibles, which before were 

 covered by the middle lobes of the low^er lip. In shape and 

 structure they are peculiar, being elongate, narrow, flat, and 

 scarcely touching each other with their crowns, which are only 

 armed with seta, and show a very small terminal surface. 

 Taking, moreover, into consideration the peculiarly restricted 

 mode of movement of the mandibles, we cannot fail to per- 

 ceive that in this case they are employed rather for the pur- 

 pose of carding the food and pushing it into the pharynx than 

 as grinding-teeth. The explanation of this arrangement and 

 of the heavy proportions of the upper lip presents itself if we 

 examine more closely the structure of the palate, whereby it 

 will appear, in the first place, that without the strong deve- 

 lopment of the upper lip the necessary space and support 

 would be wanting for the articular eminence of the mandible, 

 which in Trochalognatha is fitted into the palate ; in the se- 

 cond place, a portion of the palate just behind the mortise 

 for the articular process of the mandible will attract notice, 

 being triangular, somewhat lower than the rest, with sharply 

 defined sides, analogous to the velum palatinura of Mamma- 

 lia, and carrying a small pendent flap with rounded apex, a 

 kind of uvula, which reaches beyond the anterior margin of 

 the pharynx. To the sides of this velum palatinum the grind- 

 ing-teeth of the mandibles are closely joined ; and the whole 

 of their form is arranged to fit in with it. It is therefore 

 evident that, as above stated, they can play no other part than 

 that of carding the food and pushing it into the pharynx. 



Amongst the other appendages of the mouth, the second 

 pair of maxillae and the maxillipeds offer no essential difference 

 from those of Eleutherognatha ; but the first pair of maxillae 

 are distinguished by the following peculiarities: — the termi- 

 nal joint of the palpus is dilated, hollowed into the shape of 

 a narrow cup, with broadly truncate apex armed with short 

 coniform spines ; the outer lobe has very powerful pectinate 

 spines, whilst the inner lobe is very small, with only two hairy 

 and membranaceous appendages. 



Amongst Crustacea there exists one other Trochalognathe 

 group ; but it is in another order, namely Chilopoda amongst 



