206 MR. J. T. tlNNINGHAM OK THE [Mar. 15, 



collection, seem to exclude the possibility that any of tlie speci- 

 mens belong to that species. Further, as we have seen, the 

 characters of these small specimens agree with the brief description 

 given by S. I. Smith of the earliest ambulatory form of an American 

 species of Cancer. 



A minute examination of the specimen represented in fig. 1 

 reveals the following peculiarities : — The antei'ior portion of the 

 carapace between the eyes is much more prominent than in the 

 adult Cancer. It consists, as in the latter, of five principal pro- 

 jections or teeth, each of which carries secondary pointed teeth of 

 different sizes. The eyes are much larger in proportion than in 

 the adult, and on the anterior border of each eye-stalk is a tooth. 

 The margin of the orbit carries minute teeth. The antero-lateral 

 margin of the carapace bears altogether 10 teeth, five larger and 5 

 smaller alternating with each other. As seen in the quotation 

 giAen above. Prof. S. I. Smith states that the number of teeth in 

 the first crab-form of Cancer irroratus is only 9, 5 " normal,'" and 4 

 smaller alternating with them ; but it seems to me probable that 

 he omitted to notice the last small tooth behind the fifth large 

 tooth. In any case this tooth is undoubtedly present in my 

 specimens, and, as I shall show, its presence is of some importance. 

 The larger teeth and some of the smaller exhibit secondary teeth 

 on their hinder margins, and on these margins there are also some 

 setae. From the tenth tooth there extends backward a granulated 

 ridge corresponding to a similar ridge in the adult Cancer. 



The antennae are relatively longer than in the adult. The 

 ambulatory legs or pereiopods are similar in shape to those of the 

 adult, but the anterior pair or cbelipeds diff'er in the possession 

 of rows of pointed tubercles on the carpus and propodus, and a 

 few smaller tubercles are visible also on the dactyl us. On all the 

 pereiopods and on the antennae there are a considerable number of 

 setae. 



The length of the carapace in these smallest specimens is about 

 3 mm. ; the breadth is only 2-5 mm. We may conclude therefore, 

 both from size and characters as compared with those given by 

 S. I. Smith in reference to Cancer irroratus, that these specimens 

 are in the first crab-stage, and are derived directly from the 

 Megalopa stage. The length of the carapace in this stage is thus 

 somewhat greater than the breadth, while in the adult it is much 

 less ; even in the largest specimen in the collection here considered 

 the breadth of the carapace is 7 mm., while the length is only 

 5 mm. 



The intermediate stage seen in fig. 2 shows how the transition 

 to the adult form is effected. This stage is probably derived 

 directly from the former by a single ecdysis. In it the carapace 

 is 4 mm. in breadth and slightly less in length. The anterior or 

 rostral portion of the carapace now projects less, and the teeth 

 both here and on the antero-lateral margin have become broader 

 and rounder, while the secondary teeth on their margins have 

 become regular rounded crenations. In this condition the antero- 



