BRACHYURA. 385 



with the phenomenon recorded among the heetles. Dimorphism is illustrated hy the 

 males (h) and (c) above, but it is noteworthy that it is the larger example (r) which 

 has the more female-like form of cheliped, while the smaller one (h) has a cheliped of 

 stronelv marked male character. This seems to be a case of facultative dimorphism, 

 specimens (b) and (c) being respectively "breeding" (perhaps "low") and "non- 

 breeding" ("middle") forms. 



In length of mobile portion of the antenna, the two adult males come under var. 

 mascarena. In the ovigerous female this measurement is larger than in females of 

 the species as described by Alcock. 



The surface of the post-cardiac region of the carapace varies in character. It is 

 smooth in (6), it has a trace of granulation in (a) which is rather more obvious in (c) 

 and (</) and quite fairly developed in (e). The vertical portion of the carapace plus 

 the rostrum has in (a) and (h) a flattened surface, in (c) the lateral pair of lobes curve 

 forward somewhat, so that the anterior surface is concave from side to side. Example 

 (<?) is intermediate. 



All the specimens possess the following spines on the lateral margins of the 

 carapace : Three spines on hepatic border, one (a small tubercle) on the antero-lateral 

 branchial border, three on branchial border in the region of the epihranchial angle. 

 In addition, the two males (L) and (c) have two spines, both obsolescent in (<), and 

 anterior one so in (6), on the border between the epibranchial angle and the true 

 posterior margin of the carapace, just above the granular ridge. 



Micippa thalia (Herbst), 1803 A.l, p. 251. 



Localities : Off Mutwal Island, two specimens ; coral reefs, Gulf of Manaar, seven 

 specimens; Cheval Paar, two specimens; pearl banks, Gulf of Manaar, 18 specimens. 



Description : The specimens fall into two groups, corresponding with the figures of 

 A. Milne-Edwards (' Nouv. Archiv. du. Mus.,' viii., p. 238, pi. xi., fig. 1, 1872) and 

 of Herbst (' Krabben,' hi., pi. lviii., 3) respectively. Twenty-eight of them agree 

 verv fairly with the former and one with the latter. It may be noted that forms 

 resembling the " type "-specimen of this species have been seldom recorded. 



A. The following is the arrangement of the spines in 20 adult individuals of the 

 first variety. The number which occurs in each region with maximum frequency is 

 printed in heavy type. 



Dorsal Surface of Supra-ocular Hood. Fourteen specimens have a mere indication 

 of one granule on each hood, three have a more obvious granule, and three have a 

 small blunt spinule. 



Dorsal Surface of Branchial Region. Nineteen specimens have two spines on each 

 side (may be written 2'2), one specimen has one on the left side and two on the right 

 side (may be written 1*2). 



Gastric Region. Nineteen specimens have 2 median spines (reduced in one 

 specimen), and one has a spine and a granule. 



3 D 



