REPORT ON THE CRUSTACEA MACRURA. 



693 



does not exist in those specimens that become fully matured, and escape under natural 

 circumstances. 



The carapace is well developed, and is about a third of the length of the animal, 

 reaching as far as the extremity of the developed pereion. 



The first pair of antennas has a two-jointed peduncle that folds back against itself, 

 and terminates in two slender branches, the rudiments of the future flagella, one of 

 which is thick at the base and styliform, and the other slender and threaddike. 



The second pair of antennas consists of a single- jointed base supporting a long and 

 wide plate, the scaphocerite, which is distally 

 fringed with five or six long ciliated hairs, and 

 a slender flagellum that is about half the length 

 of the scaphocerite. 



The mandibles have not been determined. 



Posterior to the oral aperture there are three 

 pairs of biraniose appendages, which from analogy 

 with the brephalos of Crangon represent, I 

 believe, the maxillipedes and first and second 

 gnathopoda. 



The pleon is six -jointed, well developed, and 

 terminates in a broad and foliaceous plate, 

 fringed on each side of a deeply excavate median 

 cleft with five long hairs and two spines ; at the 

 base of each of the former there is a thin crenated 

 plate. 



None of the pleopoda are yet apparent even 

 in the most immature condition. 



Observation. — Whatever changes the form 

 undergoes in the development of the first and 

 second parrs of pereiopoda must take place at a stage later thai] that in which they 

 exist in the condition of the brephalos. 



Geographical Distribution. — The habitat of the original specimen described and 

 figured by Leach under the name of Atys scabra, which he afterwards changed to Atya 

 scabra, has not been recorded, but since Leach's specimen has been found to correspond 

 with Atya mexicana, Wiegmann, it may be assumed to have been found in the fresh- 

 water rivers or ponds of Mexico or the West Indian Islands. 



According to Newport and A. Milne-Edwards there are eight species of Atya already 

 known, of which Atya scabra and Atya occidentalis are from Mexico and the West 

 Indies, Atya silicates, of which a figure is given on PI. CXYTIL, is from the Cape 

 Yerde Islands, Atya robusta and Atya margaritacea are from New Caledonia, Atya 



Fig. 71.— Atya bisulcata. Telson of Zoea ; and one hair 

 from the posterior margin, enlarged to show the serrate 

 plate at its base. 



