790 W. T. CALMAN. 



0. All u audi. In both species the two forms were sharply 

 distinguished, although in the Ortmannia individuals 

 (especially in 0. All u audi) a considerable amount of varia- 

 tion was observed in the relative proportions of the fingers 

 and palm of the chelae; the Atya-form, on the other hand, 

 presented no noteworthy variation. In both species Bouvier 

 found that the dimorphism was independent of age and sex; 

 both forms were found through a wide range of size, although 

 the Atya individuals were, on the whole, somewhat larger, 

 and females of both were observed carrying eggs. In the 

 case of A. bisulcata (0. Henshawi) both forms occurred 

 in about equal numbers; in A. scrrata (0. Alluaudi) 

 there was some evidence that the relative proportions varied 

 in different localities.^ 



In one species of Caridina Bouvier found evidence of the 

 existence of an analogous mutation leading to the genus 

 Ortmannia. Among eleven examples of C. apiocheles 

 (Text-fig. 4) (probably from the Seychelles), he observed 

 one in which the carpus of the second pair of chelipeds (Text- 

 fig. 4, 5"), instead of being long and slender as in the typical 

 individuals, was short, broad, and excavated distally, re- 

 sembling that of the first pair, so that the specimen, had it 

 occurred alone, would have been referred to Ortmannia. 

 In this case, however, it remains to be seen Avhether the 



^ It may be of interest to give here the i-esults of a preliminary 

 examination of the material of these two species in the British 

 Museum collection. In one lot of Atya bisulcata obtained by the 

 ' Challenger ' Expedition at Honolulu forty-two specimens are of the 

 Atya-type and forty-six of the Ortmannia-tyise. Only one speci- 

 men cannot be referred to either, having three chelte of the Atya-shape, 

 while the fourth is distinctly of the Ortmannia-shape. There is a 

 considerable amount of variation in the chela; of the Ortmannia- 

 individuals, and their terminal brushes of seta? are always much 

 shorter than in the Atya-individuals. In a second lot of specimens 

 from Hawaii only nine Ortmannia-individuals are found among 

 thirty-eight Atya-individuals. Of the two type-specimens of Atya 

 serrata from the Cape Yerde Islands in the 'Challenger' collec- 

 tion, the larger is of the Atya-type while the smaller is a distinct 

 Ortmannia. 



