LARVAE OF DECAPOD CRUSTACEA 439 



Strikingly similar to that of Pamdirus that it is difficult to believe that this identification 

 can be correct. The Phyllosomas referred to this group are mainly Indo-Pacific and 

 attain to such extraordinary sizes as 75 mm. (Richters). Having regard to the degree 

 of development of antennae and mouth-parts in larvae of nearly 40 mm. it is probable 

 that there is a long series of later stages during which much change of shape of body and 

 of appendages may take place, and the widening of the antenna seen in the specimen of 

 37 mm. might lead to a Scyllarid form. Richters figures (pi. xxxiv, figs. 5, 6) two larvae 

 of 61 and 75 mm. which combine the Scyllarid form of antenna with the deeply excavated 

 hind-body of Pamdirus, so that it is clear that the latter character is not confined to the 

 Palinuridae and it seems necessary to accept Richters' reference of this group of Phyllo- 

 somas to the Scyllaridae. 



So far as concerns the genus to which the Discovery specimens belong only specula- 

 tion is possible, but it must be one with a representative in the western Atlantic. The 

 genus Themis must be excluded if its Phyllosoma is as described above, and of the other 

 genera of Scyllaridae only two species are known from the Atlantic : Ibacus verdi. Bate, 

 and Parribociis ursus (Herbst). The genus Pseudibacus, Guerin, is supposed by Bouvier 

 to be the natant stage of Scyllariis. As Parribacus ursus is known to occur in the Carib- 

 bean Sea and also throughout the Indo-Pacific region (De Man) it is a reasonable guess 

 that this may be the parent of the Phyllosoma in question. 



KEY TO THE FORMS OF PHYLLOSOMA HERE DESCRIBED 



a. Maxillipede 3 with setose exopod. 



i. A small rostrum present Palimrelliis}, p. ^25. 



bb. Rostrum absent. 



c. Hind-body not wider than fore-body; lengths of segments of antennular peduncle 



about as 3 : I : 2 Palinurus, p. 401. 



cc. Hind-body wider than fore-body ; antennular segments about as 2 : i : i 



Pamdirus, p. 405. 

 d. Coxal spines absent ; exopod of maxilla without setae to last stage 



Pamdirus B, p. 411. 

 dd. Coxal spines on maxillipede 3 and leg i ; maxilla with setae Panulirus A, p. 407. 

 ddd. Coxal spines large, on all legs; maxilla with setae ... Panulirus D, p. 415. 



aa. Maxillipede 3 without exopod, or with small rudiment only. 



b. Antenna slender, with long flagellum; leg 5 fully developed at early stage Jasus, p. 416. 

 bb. Antenna enlarged at base, flagellum short and broad; leg 5 generally developing late 



c. Leg 5 with setose exopod Parribacus}, p. ^^l- 



cc. Leg 5 without setose exopod. 



d. Abdomen much narrower than hind-body ... ... ... Themis'^, p. 432. 



dd. Abdomen broad at base, forming continuation of hind-body. 



e. Telson spines relatively short ; uropods rounded throughout development 



Scyllarus, p. 426. 

 ee. Telson spines long in early stages; uropods pointed in late stages 



Scyllarides, p. 427. 



