14. Mandible of the same. The palpus has been removed, f, tendon of the mandibular muscle. 



15. Mandibular palpus of the same. 



1 6. Second maxilla of the same. 



17. First maxilliped of the same, with endopodite {r i), exopodite (re), and epipodite. 



18. Second maxilliped of the same. 



19. Third maxilliped of the same, b r, gills. 



20. Proximal end of left cheliped of the sinnv, furnished with a stout hook. Seen from ventral side. 



21. Proximal end of left leg of the second pair, with two hooks, seen from ventral side. From the same stage. 



22. One of the three long curved set<e on the terminal segment of the last pair of legs of the same (see tig. 12). 



The other two setfe are destitute of the teeth with which this one is furnished. 



23. One of the abdominal limbs of the same. The endopodite is provided with hooked setK (t;), which serve to 



lock together the abdominal limbs of the two sides. 



24. Posterior abdominal appendage. No endopodite. 



25. The megalopa represented by fig. 12 passes by a single moult into the crab stage of the form represented in 



this figure, dorsal view. The eyes are much larger than in the adult, the antennae longer, and the length 

 of the carapace much greater in proportion to its breadth, and of very different outline. Breadth of cara- 

 pace, 4 mm. 



26. The same, ventral view. The form of the abdomen would seem to indicate that this specimen is a young 



male. The third, fourth, and fifth abdominal segments, which, in the adult male, are fused together, are 

 still free. 



27. Carapace of adult Ciinccr borealis, half natural size. Tlie megalopa and young cral) represented in figs. 12, 25, 



and 26 belong either to this species or to the closely allied C. irroratus. This figure is introduced to show 

 the marked difference in proportions and outline between the young and adult stages. Drawn on stone, 

 from nature, by A. Meisel. 

 28-30. Young stages of Pinnixa (Smjnna?) from Newport, R. I. From Faxon, On some Young Stages in the 

 Development o( Hippa, Porcellana, and Pinnixa, PI. IV., V. Bull. Mus. Comp. Zobl., V., 1879. 



28. Last zoea stage, .seen from above and in front, n b, penultimate abdominal segment, produced on each side 



into a rounded lobe. Through the transparent carapace are seen the rudimentary and ;is yet functionless 

 ambulatory appendages. The cross denotes the natural size. 



29. The third maxilliped and five ambulatory limbs removed from the body. VllI, endopodite of third 



maxilliped. VIII', exopodite of third maxilliped. VIII", epipodite of third maxilliped. 



30. The zoea (fig. 28) passes directly, at one moult, into the adult form sliown in fig. 30. This abbreviation of 



the developmental history whereby the megalopa stage is eliminated is very unusual among the marine 

 Brachyura which leave the egg in the zoea form. S. I. Smith has shown that another species of Pinnixa 

 passes through a megalopa stage. Some land-crabs, as has long been known, leave the egg in the adult 

 form, like Astacus among the Macroura. 



