:!7 \ CEYLON PEARL OYSTER REPORT. 



Remarks. The present specimens form a group which I helieve hreaks down the 

 distinction between Simocarcinus simplex (Dana), 1852, and S. pyramidatus 

 (Heller), 1861. As set forth by Alcock, the characters by which the former is 

 distinguished from the latter are (1) the much shorter rostrum of the male; (2) the 

 presence of three tubercles, disposed in a triangle, on the gastric region ; (3) the 

 larger and more prominent eyes; (4) the absence of the lobule on either side of the 

 posterior border of the carapace ; (5) the much more massive chelipeds of the male. 



In the first place, I may remark that the only other specimen which appears to 

 agree with the single one for which Heller created pyramidatus is the male 

 described by Alcock. I have examined Miers' specimens of S. simplex in the 

 British Museum and find that, though they are evidently S. simplex in the narrower 

 sense of the term, they show two points of difference from Dana's figure which 

 diminish the value of distinctions (3) and (4) above. There is in each of them a lobe 

 at either end of the posterior border (it is distinct, though not so large as in Heller's 

 figure of S. pyramidatus), and in all the males the eyes are less prominent than in 

 Dana's figure. This doubt cast upon the value of distinctions (3) and (4) is confirmed 

 by the present specimens (see description above). The fifth distinction seems, in view 

 of the evidence of the specimens in the present collection, to be one between young 

 and adult males or between non-breeding and breeding adults. There is, however, 

 some difference between the massive chela of male specimens (a) and (b) of the present 

 examples and that of the British Museum male (m) ; this may or may not be a 

 difference associated with high and low males respectively. Of Alcock's two 

 remaining distinctions, (1) and (2), each specimen of the present group unites the 

 three gastric tubercles of S. simplex with the long rostrum of S. pyramidatus. 

 Cano ('Boll. Soc. Nat, Napol.,' hi., 188!), p. 173) describes an animal with a similar 

 combination and unites the two species. More recent writers have not followed him, 

 and Klunzinger (p. 19) describes a similar male as pyramidatus. The additional 

 evidence confirms Cano. 



It is difficult to estimate the value of the character rostrum-length referred to 

 above. It holds excellently as between the present individuals and the specimens 

 labelled S. simplex in the British Museum (see measurements above); but in 

 Klltnzinger's figure the index E.l. -t-C.1. seems to be about 0-62, and Henderson 

 describes his specimens as simplex, but with longer rostrum. The high variability of 

 this character in S. camelus, Klunzinger (11)06, pi. i., tigs. 2a-g), is to be borne in 

 mind. A further point of difference between my specimens and the British Museum 

 examples of & simplex is the greater length of the first pair of walking legs in the 

 former (see measurements above, under W.L.I. 1. -M '.1.). The present forms and all 

 those with the three gastric tubercles I name var. pyramidatus. 



I consider that Miers' distinction between Simocarcinus and Trigonothir (the latter 

 genus formed for a single male specimen! must be given up. The slender cheliped of 

 the latter is better considered as the character of a young or of a non-breeding 



