of Recent Species of \a\\\\x\\x?,. 259 



constajitlv in the American and Oriental species*. On tlie 

 supposition that the opcrcuhim was originally simihir to the 

 appen(hi^-es that follow it, there can be no question that the 

 American species possesses a more primitive type of this 

 appendage than the Oriental. In the former the endopoditi 

 ends in a free movable segment, representing the two distal 

 segments of this branch seen in tiie branchial appendages. 

 In the Oriental species, on the other hand, the three segments 

 of the endopodite of the branchial a|)pendages are representel 

 in the operculum by a triangular segment fused externally 

 to theexopoditeand mesially to its fellow of the opposite sidef. 



In the branchial appendages of the opisthosoma the wart- 

 like sensory organs on the endopodite are fairly constant in 

 number and position in all the species. Typically there are 

 five, placed as shown in PI. VI. fig. 6, but the smaller 

 of the two on the distal segment is sometimes, perhaps 

 generally, wanting in rotandicauda. 



1 find one slight difference in the endopodites between the 

 American and Oriental species. This is the presence in the 

 former of a small movable spine on the inner distal angle of 

 the peimltimate segment (PI. VI. fig. 7). This spine is 

 absent in the Oriental species. 



In the development of secondary Sexual characters the 

 American species is again less specialized than the Oriental. 

 In the former only the second appendage of the prosoma is 

 modified as a clasper and there is no variation in the spines 

 of the opisthosoma in the female. In the Oriental, on the 

 other hand, the second and third pairs of appendiiges of the 

 prosoma are converted into holders in the male and the three 

 posterior spines of the opisthosoma in the female are markedly 

 shorter than the anterior, especially in Tachypltus. Carcino- 

 scorpius, in this respect, is less specialized, as also it is in the 

 chelate condition of the claspers, a peculiarity which clearly 

 preceded the heraichelate condition of these appendages 

 observable in Xiphosura and lachi/pleus. 



* Owiug to au error iu specific determination, Dr. II. Woodward (PaL 

 Soc, Merostoniata, pt. iii. p. 115, 1872) rej^arded these differences as 

 relei-able to sex, assigning the operculum of L. rotuiidicauda or L. moluc- 

 caniis to the male of L. polyphemus, and the operculum chiira'-teristic of 

 both sexes of L. polyphemus to the female of that species. Lalreille was 

 apparently the tirst to set this error rolhng. 



t Except in the spjcies identified by lloeven as L. moluccanus (see 

 p. 264), wht;re the two appear to remain unf used iu the middle line. 



