1. '08. 53 



arthiobranch of the third maxillipede and the arthrobranch 

 over the base ol' the fourth pereiopod ; both, however, are in- 

 dicated by papillae. The complete series of gills is found in 

 an example of 38 mm. 



The extremely late development of the mandibular palp is 

 one of the most interesting features of the development of this 

 species. In specimens of 30 mm. and under no trace of it can 

 be found, while in examples of 33 and 38 mm. it is present 

 only as a simple lobe (fig. 21), without trace of subdivision 

 or of setae. In the Irish collection the two-jointed mandi- 

 bular palp, so essentially characteristic of the genus Parapa- 

 siphae, is found only in the two largest specimens, measuring 

 44 and 47 mm. 



The sulcar depression on the dorsal carina of the carapace 

 is evident only in specimens of '28 mm. and upwards. 



Several points in the development of P. sulcatifrons are 

 rather remarkable, and call for special mention. 



Throughout the metamorphoses the length of the rostrum 

 remains practically unchanged in its relation to the other 

 parts; the eyes, on the other hand, which are at first almost 

 obsolete, gradually increase in proportional length, and in the 

 later stages reach beyond the apex of the rostrum. Black 

 pigment is absent throughout and it is only in specimens of 

 16 mm. and upwards that the corneal portion is differentiated 

 from the stalk and shows traces of the obscure facets found in 

 the adult. 



The apex of the telson is at first emarginate, then definitely 

 convex ; later, it is again found to be emarginate, while in the 

 adult it is once again convex. The very broad larval telson 

 rapidly narrow^s down to the adult form in the course of a few' 

 moults, during which the total increase in length of the speci- 

 mens is insignificant. 



The late development of the arthrobranchs, the complete 

 series of which are only present in specimens of 38 mm. and 

 upwards, is in accordance with what was previously know^n in 

 the case of the closely related genus Pasiphae (cf. Caiman, 

 1903). The retention of exopods on the first two pairs of 

 maxillipedes until a comparatively late stage is rather remark- 

 able, but much more astonishing is the complete absence of 

 the mandibular palp in specimens 30 mm. in length, and its 

 rudimentary, one-jointed, condition in examples of 33 and 

 even 38 mm. The possession of a one or two- jointed palp is 

 a most important generic distinction in the family Pasi- 

 phaeidae, but its rudimentary character in the present species, 

 in a specimen in which even the branchiae are fully developed, 

 indicates that considerable caution is necessary in its use in 

 examples which are not clearly recognised as adult. 



If, as seems probable, the specimen of 8'5 mm. represents 

 the earliest free larva, the metamorphosis of P. sulcatifrons, as 

 might be expected in an abyssal species bearing large eggs, is 

 considerably curtailed. The presence in the specimen of all 

 five pereiopods (though only in the form of buds) renders the 

 term zoea inapplicable ; the change from the true zoea to this 

 stage is doubtless effected within the egg. 



