322 S. I. Smith — Early Stages of Hippa talpoida. 



tooth is a little more anterior than the others, while on the left side it 

 is more posterior, so that these inferior marginal teeth overlap each 

 other when the mandibles are brought together. The posterior 

 side of the crown of the right mandible is slightly convex while the 

 same side of the left is a little concave. On the superior half of the 

 crown of each mandible there is a series of six slender processes, or 

 teeth, of which the live inferior are very slender, setae-like, and twice 

 as long as the two triangular teeth just mentioned, while the superior, 

 or marginal, one is stouter, acutely triangular, and divided at tip. In 

 the specimen figured, there is also a small supplementary tooth on the 

 right mandible, between the bases of the third and fourth processes of 

 the superior half of the margin. 



The first pair of maxillae (Plate XLVI, fig. 5, e; and fig. 12) have 

 changed scarcely at all, except in size, from their simple form in the 

 second stage. The inner lobe has a single rudimentary seta, on the 

 inner edge near the tip, in addition to the three terminal ones, the 

 three teeth of the outer lobe are relatively a little shorter and very 

 slightly stouter, and the palpus is considerably larger. 



The second pair of maxillre (Plate XLVII, fig. 2) have advanced 

 considerably in their develoj^ment and have apparently partially 

 assumed their adult function. The protognath shows a slight indica- 

 tion of division into two lobes {ci^ h, fig. 2), of which the outer projects 

 as far forward as the scaphognath, from which it is much more deeply 

 separated than in the earlier stages. The scaphognath is twice as 

 long as the protognath, and its posterior portion is elongated and 

 narrowed at the extremity as in the later stages, but its inner edge is 

 not yet margined with the characteristic plumose setse. 



The first and second pairs of maxillipeds (Plate XLV, figs. 2 and 4, 

 and Plate XLVII, fig. 5) have the same form and structure as in the 

 preceding stages, the only noticeable difiference being the addition of 

 still another pair of setse at the tip of each exognath, making twelve 

 in all, of which the outer are scarcely more than half as long as the 

 middle ones, which are not quite equal in length to the exognath 

 itself. 



The third pair of maxillipeds and all the thoracic limbs (Plate 

 XLV, fig. 4, and Plate XLVIII, fig. 9) are still curved inward 

 beneath the sternum and entirely inclosed within the posterior por- 

 tion of the carapax, although the four anterior pairs of legs have 

 begun to show clearly the form which they assume in the megalops 

 and later stages. The third pair of maxillipeds (J, Plate XLVIII, 

 fig. 9) are still sub-cylindrical and in each the meral segment is only 



