BORRADAILE— ON THE PONTONIIN^ 335 



nearly horizontal, with its width longitudinal in the body. The other — the molar 

 process — is stout and subrectangular in section, and slants dorsally, to end obliquely 

 truncated on the median plane. In Urocaridella (Plate 53, fig. 2 d") and Palcemonella 

 (Plate 53, fig. 5 d"), a short, two-jointed palp is present, standing on the anterior side of 

 the limb, at the base of, and just dorsal to, the incisor process, behind which it is partly 

 hidden in ventral view. The incisor and molar processes perhaps represent the first 

 two endites of the primitive crustacean appendage*. The palp represents the rest of 

 the protopodite and the endopodite. Its first joint is probably the basipodite, but, in 

 view of the facts of meristic variation, it is doubtful whether there would be any validity 

 in such a statement as that the second is the ischiopodite. Still less can the third joint 

 be regarded as the meropodite alone. 



The incisor process usually ends in three teeth, the middle one of which is shorter 

 than the others, but the intermediate teeth may be more numerous and sometimes differ in 

 number on the two sides. Thus Gorcdliocaris japonica has tAvo on one side and three on the 

 other, while in Concliodytes meleagrincB (Plate 57, fig. 26 d) there are three and four, nearly 

 equal to the outer teeth. The molar process ends in a roughly square, concave surface, 

 surrounded by an incomplete wall made up of projecting lobes, from four to five in number. 

 All but one of these have crescentic or horseshoe-shaped rims, open towards the middle. 

 The remaining lobe has an unbroken rim, and a great part of its circumference is beset 

 with a fur of bristles or a rough patch of tubercles. Opposite this lobe the wall is lower 

 than elsewhere, and in the left mandible is also roughened. This roughening of the molar 

 surface is, I think, the last remains of the clothing of bristles described for the Alpheidse 

 by Oouti^ret, who also figures in some cases an oval isolated area on one side of the 

 process. The ridges which in Amphibetwus and some Hippolytidae represent a part 

 of the bristly surface may perhaps be transitional between this condition and that 

 found in Desmocaris (p. 327). There are only very slight traces of a roughened 

 surface in Leander, so that possibly the possession of a considerable extent of such a 

 surface should be added to the list of primitive characters of the Pontoniinte which 

 are not found in Palaemoninse. The lobes differ a good deal in shape, and there 

 is only a general correspondence between those of the mandibles of the two sides. So 

 far as this correspondence goes, it is not the mirror-likeness usually found in paired 

 structures, but the two arrangements are reversed, so that the rough lobe of each molar 

 process overhangs the lowest part of the edge of the other and the surfaces interlock. 



The mandibles lie in a chamber enclosed between the lips (Plate 57, figs. 26 s and t), 

 the hood-like upper lip (labrum) standing in front of them and the large, bilobed lower lip 

 (metastoma, Plate 52, fig. 1 q) behind, while the swollen bases of the mandibles themselves 

 close in the chamber at the sides. There are two openings to the lip chamber — a 

 narrow median slit between the lobes (paragnatha) of the lower lip, and a wider 

 transverse gap between the upper and lower lips. The incisor processes close the 



* On the other hand, the incisor process may be merely an outgrowth from the molar process 

 (gnathobase). An interesting analogue to it is seen in the ilange at the end of the grinding surface of 

 the mandible of Apus. As it stands, this flange is on the hinder side of the limb, but the shape of the 

 mandible gives reason to suppose that it has been rotated backwards. 



t Ann. Sci. Nat. Zool. (8), ix. pp. 152—157 (If 



