538 THE VOYAGE OF H.M.S. CHALLENGER. 



The branchial arrangement, as I have observed it in the specimens of Alpheus 

 edwardsii from the Cape Verde Islands, may be tabulated as follows : — 



Pleurobrancliise, . . . 1 1 1 1 1 



Artlirobrauchiae, . . . ... 1 



Podobranckias, . . . 



Mastigobranckiae, . . . r r v r r r ... 



h i k 1 m n o 



The mastigobranchise are all rudimentary in appearance, but they evidently have some 

 office to fulfil, since they terminate in a strong and peculiarly shaped hook. 



The branchial plume belonging to the second pair of gnathopoda is small, and 

 consists of a bundle of leaflets attached to the flexible membrane of the coxal 

 articulation. 



Development. — The brephalos in this genus may be a Zoea or Megalopa. In the 

 Zoea (PI. LXXXIX. fig. 4) there is neither rostrum nor dorsal tooth, and the ophthalmo- 

 poda are large. The figure is from a specimen obtained direct from the parent by Mr. 

 Power, from a species resembling Alpheus neptunus, Dana, procured at the Mauritius. 

 The ophthalmopod is orbicular and consists of the ophthalmus only. The first pair of 

 antennas has a single-jointed peduncle and two small branches, one being a long plumose 

 hair, the other short, conical, and carrying three membranous cilia. The second pair of 

 antennae consists of a peduncle, flagellum, and scaphocerite which is multiarticulate 

 and fringed with hairs. The oral appendages I have not examined, but they are 

 succeeded by three pairs of biramose apppendages, by the deciduous representatives of 

 the third pair of siagnopoda, and the first and second pairs of gnathopoda. Posterior to 

 these there appear to be no other appendages either on the pereion or pleon. The telson 

 terminates in a broad fish-tail fan, fringed with ciliated hairs and flanked by a simple 

 spine at each extremity. A specimen which I consider to be the young of this genus 

 was taken at the surface, off the African coast of the Atlantic, on April 13, 1876, 

 apparently only recently hatched. 



In some species the brephalos appears to be in a more advanced form and is hatched 

 in the Megalopa stage (PI. CXXII. fig. 1), and this distinction occurs in species very 

 closely resembling those producing the Zoea form. 



This peculiarity of development was first described by myself in a memoir with 

 drawings communicated to the Eoyal Society, 1 from specimens obtained by Mr. Power in 

 the Mauritius, and the fact has since been confirmed by Mr. Packard. 2 



The original of my drawing is 2 mm. in length and was procured from a specimen 

 14 mm. long, resembling the figure that I have given of Alpheus minus, Say. 



The carapace is about one-fourth the length of the animal and has no rostrum. The 



1 Proc. Roy. Soc, vol. xxiv. p. 375, 1876. 2 American Naturalist, vol. xv. p. 788, 1881. 



