MACRURA. SCII MITT. 327 



"PEN\US MASTERSII." 

 (Plate Iviii., figs. 1-2.) 



Alcock correctly inferred that this species probably 

 belonged either to the P. affinis or P. deschampni group; 

 an examination of the cotype shows that it belongs to 

 the former, or P. monoceros group, as it is sometimes 

 also designated. Haswell's cotype is immature, the two 

 halves of the petasma being separate, undeveloped and 

 simple, but a faint notch and tubercle on the merus of 

 the left fifth leg the right is missing gives unmistak- 

 able evidence as to its true position. The dactyl of 

 this leg is missing, but apparently it would not have 

 reached the tip of the antennal scale. 



This cotype is 71 mm. long from the tip of the telson 

 to the end of the damaged rostrum. The carapace, exclud- 

 ing the rostrum, is 16 mm. long, and the rostrum, from 

 which the tip is gone, measures 10 mm. in length. The 

 only feature in Haswell's description of P. mastcrsii 

 which could differentiate that species from P. monoceros 

 is the "smooth carapace'' but on the carapace of this 

 immature male, there are ample evidences or traces of 

 tomeutum, which seems to have been largely rubbed off. 

 In some of the depressions on the abdomen also there 

 are traces of former pubescence, particularly on the fifth 

 and sixth somites. When wet, this rather scanty pubes- 

 cence is not very noticeable, which evidently explains 

 why the carapace was originally described as smooth. 



The other three specimens from Finche's Bay, Cook- 

 town (Reg. No. P. 4287) are all small and more or less 

 immature. The smallest, 47 mm. long, is a female, and 

 its thelycum resembles that of an immature P. monoceros. 

 The median anterior grooved "tongue" is rather wider 

 posteriorly than anteriorly, which is the reverse of what 

 is usual in larger specimens of P. monoceros \ in a large 

 female of 160 mm. from Mauritius, however, this "tongue'' 

 is widest at the middle of its length. The ear-like lobes 

 bounding the postero-lateral angles of the thelycum are 

 rather more medial than one would expect to find in 

 a monoceros, but an examination of a series of females, 

 the smallest of which is a specimen from Formosa about 

 62 mm. long, indicates that their position varies with 

 growth. In the course of development or growth of the 

 thelycum, the ear-like lobes change from a transverse 

 medial position to an almost wholly lateral one; further, 



