370 CEYLON PEARL OYSTER REPORT. 



the tubercles of the carapace ; (2) the measurements, as given above ; (3) the extent 

 to which, if at all, the rostral lobes are ajmosed. Though all appear apposed to the 

 naked eye, variation is seen by aid of a lens. In (a) and (c) they are apposed 

 throughout their length, in (d) and ( f) they are apposed distally, but are separated 

 proximally by a narrow space, and in (6) and (e) they are separate throughout their 

 whole length. 



In the single male specimen the cardiac tubercle is, as in the females, the largest ; 

 but the median gastric and the posterior branchial tubercle of either side are all of 

 approximately the same size, the former being relatively smaller and the latter 

 relatively larger than in the female specimens. All the segments of the cheliped are 

 longer and more swollen than in the females ; their denticles are present, very small 

 and set well apart. The lingers are apposable distally for rather less than half their 

 length, a hiatus being left proximally, which is more or less bridged by a couple of 

 hlunt teeth, one near the base of each finger, that of dactylus distal to the one on the 

 fixed finger. 



I judge Achwus dubia to be closely allied to A. tcnuicollis, differing from it mainly 

 in the following particulars: (l) Neither tubercles, rostral lobes, chelipeds, nor 

 sternal surface bear spinules ; and (2) Character of rostral lobes. 



The rostral lobes are noteworthy. They are more sharply pointed than, one expects 

 in Achceus, making an approach thus to Steuorhynchus, e.g., S. rostratus, where they 

 are shorter than usual. The essential distinction hitherto recognised between Achceus 

 and Stenorhynchus has been that in the former the rostrum consists of two short lobes, 

 and in the latter of two long spines. 



Paratymolus hastatus, Alcock, 1895 A.1, p. 174 ; A.Invest., pi. xviii., fig. 4. 



Locality : Gulf of Manaar, six specimens (three adult males, one young male, and 

 two adult females, one ovigerous). 



Description : C.l. (exclusive of rostrum) of an ovigerous female = 5 '25. 



In the above females the genital orifices are, as in Alcock's specimen, on the sternum, 

 not on the bases of the 3rd pair of walking legs. 



Remarks. Alcock observes that the position of the genital orifices of the female 

 as above confirms Ortmann's view that the correct place for this genus is among the 

 . leJueus-likti Maikke. 



Oncinopus aranea, de Haan, 1837 A. 1, p. 183. 



Localities : Trincomalee, one specimen (ovigerous ? ) ; pearl banks, two specimens 

 (adult c? and ovigerous ? ) ; coral reefs, Gulf of Manaar, three specimens (ovigerous ? , 

 adult c? , and young 6 ) ; south of Galle, deep water, one specimen (with Sacctdina). 



Description : C.l. (including rostrum) of an ovigerous female = 8"50. 



lii-marks. One of the ovigerous females which bears a parasitic Sacculina retains 

 the usual broad female type of abdomen, and its abdominal appendages are also well 

 developed. 



