378 M. E. L. Bouvier on the Genus Ortmannia, Eathb., 



chelse are alone modified, then to Ortmannia, M. Rathbun 

 {Atyoida, Ortraann), in which the modifications take place 

 in the chelae o£ the first two pairs of feet, and at last one 

 comes to the terminal forms of the family, the Atya, of which 

 the very curious chela? are split right down to the base and in 

 consequence are devoid of a palmar region. Further, in the 

 genus Atya itself it is possible to establish a series of species 

 which progressively depart from Ortmannia. By its small size 

 and its rostrum, subtiiangular and toothed below, A. serrata 

 presents some resemblance to Ortmannia mexicana, Sauss, 

 (0. potimirim, F. Mil Her), whilst A. gabonensis, Giebel, 

 A. robusta, A. Milne-Edwards, and many other forms stand 

 out at first sight by their very marked adaptive characters : 

 large size, rostrum laterally serrated, feet of the third pair 

 singularly strong and robust, &c. 



It appears that Ortmannia is separated from all species 

 of Atya by two very constant characters: on the one 

 hand, the form of the chelae, which are normal, with a 

 relatively short mobile digit and a well-differentiated palmar 

 region; on the other, the development of the carpus, which 

 is longer than wide, at least in the feet of the second pair. 

 These two characters are of the first importance; they 

 bring tcgether Ortmannia, Caridina, and Atyaphyra, whilst 

 they separate them considerably from the Atya. 



In studying the Atyidse in the collection of the Museum, 

 a batch of shrimps, collected at Honolulu by M. Ballieu, 

 particularly attracted my attention. These shrimps were 

 Atyidse of small size, all adult, and in other respects very 

 much alike ; but some presented all the characters of Atya 

 bisulcata, Sp. Bate, whilst others belonged very clearly to 

 the genus Ortmannia. 



In 1901, Miss Mary Rathbun made an analogous observa- 

 tion on the Atyidse collected on the Sandwich Islands by 

 Mr. Henshaw ; she grouped in the species of Sp. Bate all 

 the examples with short carpi and chelse split down to the 

 base ; the others she regarded as types of a new Ortmannia, 

 0. Henshawi. I found myself confronted by the same 

 forms, but I was led to regard them quite differently from 

 Miss Rathbun. 



Setting aside the generic characters affecting the carpi and 

 chelse, these two forms resemble one another in all respects : 

 same structure of rostrum, antennse, buccal appendages, same 

 tegumentary ornaments, everywhere the most absolute 

 identity — somewhat strange in species belonging to different 

 generic types. More than this, the two forms have that 

 similarity of appearance which characterizes all the repre- 

 sentatives of a single species, and which, in the deter- 



