REPORT ON THE CRUSTACEA MACRURA. 251 



monodon, whereas in the specimens now under our observation in the Challenger 

 collection, taken in the same haul, the female has a median groove, but in the male there 

 is none, the dorsal carina being entire. 



There are, however, some minute details that are at variance, although not sufficiently 

 important to justify specific separation. 



Both Penseus monodon and Penseus semisulcatus carry three teeth on the lower 

 margin of the rostrum, but according to de Haan's figure they are situated, or at least two 

 of them, posterior to the most anterior tooth on the upper margin, whereas in our 

 specimens of Penseus monodon, they are all in advance of that position. In de Haan's 

 figure there is also shown what may be considered as a supraorbital tooth, but judging 

 from the specimens I have examined, it is rather the result of a somewhat sudden curve 

 or bend in the orbital margin than a distinct tooth. 



Desmarest has evidently mistaken the species, for he says that it has seven teeth 

 on the upper margin of the rostrum and five below. Mdne-Edwards says that it has 

 eight or nine teeth above and three below ; and de Haan says that it has eight teeth 

 on the upper margin and three below. In the Challenger collection there are four 

 specimens, all of them adult. Three of these are females and one is a male. The females 

 have seven teeth on the dorsal crest, the male six, and all have three below. Mr. Miers, 1 

 of the British Museum, says in relation to this species that he thinks it to be synonymous 

 with de Haan's species, Penseus semisulcatus. Moreover, he says, "In two specimens 

 from Australia (Shark Bay) and one from Ceylon, the rostrum is 6-7-toothed above, 

 the teeth towards the apex separated by much wider intervals than in the other specimens 

 referred to P. semisulcatus, there is a short dorsal carina which does not reach to 

 the posterior margin of the cephalothorax, and is not canaliculated above, and the gastro- 

 hepatic sulcus is very deep and strongly defined." For the latter he proposes the name of 

 Penseus monodon if the two species be distinct. 



Such a difference can scarcely be recognised as a specific character, for the greater 

 enlargement of the interdental spaces may be and probably is induced by age, sex, or 

 local variation; and, as I have shown above, the postrostral groove cannot be accepted as 

 more than a collateral feature, since it is found in the females and not in the males of 

 the same species. 



The flagella of the first pair of antennae are subecpial, whereas Penseus semisulcatus 

 is described by the author as having the internal branch twice the length of the 

 external. 



De Haan described the female as having the sternum between the posterior pair of 

 pereiopoda divided by a median cleft and reflexed. (" Sternum feminarum inter pedes 

 cuiintos rima media continua divisum et reflexum.") These exist as two flattened 

 calcified plates — which I distinguish by the name of thelyca — extending from the base 



1 Proc. Zool. Soc. Lond., p. 299, March 5, 1878. 



