REPORT ON THE CRUSTACEA MACRURA. {> 



tenuity. Those of the throe following pairs are also biramose, but the inner branch is 

 short and broad; the outer is long and wide, being bent over the inner; the margins 

 are smooth, inflected, and fringed with a delicate ciliary growth. In Callianidea the 

 second pleopoda resemble those of the three succeeding pairs. They are biramose and 

 foliaeeous; the margins, instead of being fringed with small hairs or cilia, have these 

 modified into soft and flexible articulated membranous filaments. These, it is assumed, 

 are true branchial appendages ; 1 lut whether they fulfil the function of aeration of the tissues 

 or not, it appears to me that in classification they can only be regarded as finely modified 

 hairs, and, consequent]}', are only of generic import. The genus Issea of Guerin, which 

 Milne-Edwards changed into Callianisea, because Guerin's name had previously been 

 in use, and which has again been changed by Dana into Callisea, to prevent the con- 

 fusion likely to ensue from the resemblance between Callianassa and Callianisea, appears 

 to me to have been founded upon a damaged specimen of Callianidea, The character 

 assigned as a distinctive feature was the presence of only one branch attached to each 

 pleopod ; but the imperfect condition of the specimen examined induced Milne-Edwards 

 to suggest that this arrangement was the result of an accident. The only distinction 

 between Callianidea and Callianisea of Milne-Edwards (the latter being Issea of Guerin), 

 rests upon the author's statement that the pleopoda are furnished with a great 

 number of little branches grouped together. Or, to use his own words: "garnie d'un 

 grand nombre de ramuscules en form de grappe," which Milne-Edwards supposes to mean 

 that the ramuscules were inserted together directly on the base of the pleopoda. 



An examination of the structure of the pleopoda in Callianidea, which is incorrectly 

 figured by Milne-Edwards, 1 shows that the ramuscules are massed together, forming a 

 bundle attached to the margin of the base of the inner branch of the pleopoda, not to the 

 peduncle, as suggested by Milne-Edwards. 



The branchiae of Callianassa and Callianidea resemble each other, and appear 

 to form a transition between the trichobranchiate and phyllobranchiate types. They 

 consist of long and narrow filaments, which are closely packed and laterally com- 

 pressed, they are arranged in two longitudinal rows, and differ from those of Cheiro- 

 platea in being more numerous, and are consequently compressed instead of being 

 cylindrical. 



The genus Axius, while still retaining some of the features, more especially in external 

 aspect, of the Thalassinidse, exhibits a character that approximates its species to those 

 that belong to the family of Astacidse. 



For example, the podobranehife arc present, being attached to several of the pereiopoda, 

 and, according to my observation, in Paraxius and Eiconaxius the mastigobranchiae are 

 present to an equal degree, and form a consistent feature in leading us gradually to 

 the family Thaumastochelida?, in which all the branchiae and their mastigobranchial 



1 Hist. Nat. des Crust, pi. xxv. Ms, fig. 14. 



•(ZOOL. CHALL. EXP. PART Lit. 18SG.) 1'" '-' 



