Crustacea Decapoda and Stomatopoda. 295 



river in the Siamese Malay States. The females are from 76 to 117 mm. in length and 

 the male y^ mm. 



In both sexes the rostrum is more elevated at the base than in Alcock's figure ; in 

 the male it reaches only a little beyond the eyes, whereas in the female it is much 

 longer, extending to or a trifle beyond the end of the antennular peduncle. Alcock 

 has not noted any difference between the sexes in the proportionate length of 

 the rostrum, but some of the females determined by him are in close agreement with 

 those in the present collection. The petasma agrees almost exactly with Alcock's 

 figure. The thelycum varies considerably, more especially as regards the size of the 

 central plate between the bases of the fourth legs. 



Family SERGKSTIDAE. 

 Genus Acetes, Milne-Edwards. 

 The characters of the different species of Acetes have hitherto been very imper- 

 fectly known, and the determination of the three forms in the collection proved in 

 consequence to be a matter of some difficulty. It was only after an examination of 

 the long series of undetermined specimens in the Indian Museum that definite conclu- 

 sions were reached. The results of my examination of this material (with which that 

 collected by Dr. Annandale is included) have been published in the Records of the 

 Indian Museum. In this paper Milne-Edwards' A . indicus is redescribed and figured 

 along with A . erythraeus, Nobili, A . japonicus, Kishinouye, and a hitherto unknown 

 form from Borneo. In three of the 'Species well marked sexual differences are to 

 be found in the length of the last segment of the antennular peduncle. In the fourth 

 species, A . erythraeus, Nobili, the males appear to be dimorphic in respect of the pro- 

 portionate length of this segment, the specimens on which this interesting observation 

 is based forming part of Dr. Annandale' s collection. 



Acetes indicus, Milne-Edwards. 



1917. Acetes indicus, Kemp, Rec. Ind. Mus., XIII, p. 47, text-figs. 

 The specimens in Dr. Annandale' s collection are from the Tale Sap. Eleven 

 examples were obtained in the channel between the inner and outer lakes in the 

 ■ vicinity of Pak Raw and Pak Payun, the specific gravity of the water varying from 

 1-0015 to 1-00225 (corrected). Four individuals were also found at the mouth of the 

 outer lake near Singgora in company with Acetes japonicus, the specific gravity of the 

 water here varying from 1-004 to 1-0085. 



Acetes erythraeus, Nobili. 



1917. Acetes erythraeus, Kemp, Rec. Ind. Mus., XIII, p. 51, text-figs. 

 This species is represented in the collection by four males from the mouth of the 

 Prai. river, opposite Penang and by a few of each sex from the Patani river, below the 

 town of Patani in the Siamese Malay States. In the latter locality the species 

 was found with Acetes japonicus, occurring in water that was quite fresh, though in a 

 situation subject to tidal influence. 



