jg22.] S. Kemp: Notes on Crustacea Decapoda. 259 



Two of the specimens, which were found together in a large 

 Tridacna, were transparent when alive and dotted all over with 

 pale green chromatophores. The female bore green eggs. The 

 third specimen also found in Tridacna, was transparent with red 

 chromatophores ; it differs structurally from the other two in the 

 cornea of the eye, which is blacker and distinctly wider than 

 the stalk. 



The affinity of this small species with A . miersi is clearly shown 

 by the similarity in structure of the dactyli of the last three legs. 

 Borradaile's Anchistus biunguiculatus also possesses biunguiculate 

 dactyli, but their detailed structure has not been described. In 

 this species, however, the rostrum is toothless and the fixed finger 

 of the second peraeopod is straight and is much shorter than the 

 dactylus which is strongly hooked at the end. In A. miersi and 

 A . demani the fingers are of equal length and both have inturned 

 tips. 

 C 419,1. Port Blair, Andamans. S. Kemp, March, Two, Types. 



■9I.S- 

 C 420/1. Port Blair, Andamans. S. Kemp, Feb., One. 



1921. 



The specimens were all obtained from Tridacna, found at low 

 water on the shore at Aberdeen. 



Genus Pontonia Latreille. 



1917. Pontonia, Borradaile, Trans. Linn. Soc. (2) Zool. XXII, p. 389. 



This genus comprises species which live either in the mantle 

 cavity of lamellibranch molluscs or in the branchial sac of ascidians. 



In structure Pontonia closely resembles Anchistus, with which 

 it agrees in the very broad and hairy inner lacinia of the maxillula. 

 The species of Pontonia are, however, rather more depressed in 

 habit and the rostrum, though it may be dorsally carinate and 

 with a small ventral keel near the tip, is always toothless and 

 never exhibits the strong lateral compression found in the related 

 genus. The two distal segments of the third maxilliped are 

 frequently but not always broad and the plane of their greatest 

 breadth, as in Conchodytes, is more or less at right angles to that 

 of the preceding segment. This curious disposition is brought 

 about either by a twisting of the antepenultimate segment or by a 

 torsion at the articulation between the penultimate and ante- 

 penultimate segments. The dactylus of the last three legs is simple 

 and not strongly hooked, or biunguiculate, sometimes with a series 

 of spines along the posterior margin. There is a tooth or spine at 

 the distal end of the last abdominal somite on either side of the 

 base of the telson and the postero-lateral angles are acutely pro- 

 duced. The dorsal spines of the telson are usually large. 



The antennal spine, as in Anchistus, is present or absent. The 

 distal endite of the maxilla is divided into two lobes in the typical 

 species, P. iyrrhena, but is slendw and undivided in the Indian 

 forms. 



