27 



is sometimes hardly distinguishable. Usually there is a blunt 

 conical tubercle on the front of the eyestalk and this may possibly 

 represent the remains of the eye itself. 



The oral appendages are similar to those of Polycheles. 



The pereiopods are also on the same plan as in the last genus, 

 but the chelipeds are shorter and there are differences in the 

 arrangement of the spines. 



Except on the first abdominal segment, where they are modi- 

 fied in the usual manner in adults, and are small and slender in 

 immature individuals, the pleopods are long and well developed. 

 There is an appendix interna with distal booklets on the endo- 

 podites. 



The telson and uropods are very similar to those of Polycheles. 



The branchiae are as described by Faxon, formed of a stem 

 which gives off long delicate filaments which decrease in size 

 towards the tip. .In the specimens which I have examined the 

 epipodite of the third maxillipedes is large and well developed, 

 but those of the first four pairs of pereiopods are very small 

 and feeble. The branchial formula is as follows : — 



— VII. VIII. IX. X. XI. XII. XIII. XIV. 



Podobranchs. ep. — ep. 1+ep- 1+ep. 1+ep. 1-f-ep. — 



Arthrobranchs. — — 1? 2 2 2 2 — 



Pleurobranchs . — — — — 1 1 1 1 



I have been unable to find any trace of an arihrobranch 

 on the third maxillipedes. In speaking oiPolychele'^ Alcock says 

 that this is sometimes very small and may be altogether absent, 

 and it would seem as if the same were true of Eryonicus for Faxon 

 mentions the arthrobranch in his description. 



It has been suggested by mxore than one author that these 

 interesting crustaceans are not adult forms, but are merely a 

 stage in the development of Polycheles. This view was put for- 

 ward by Spence Bate in his original description, and has been 

 supported by some on the ground that no specimen has been 

 found bearing ova, that the first pleopods are of an immature 

 type, and that the whole aspect of ths animal is that of a larval 

 form. On the other hand, Faxon had in his collection a specim.en 

 measuring 62-5 mm., and another of 40 mm., and it is difficult to 

 believe that animals of such large size should be merely larval 

 forms, especially when we know that perfectly formed specimens 

 of Polycheles have been found measuring no more than 30 mm. 

 Moreover in Faxon's largest specimen he showed that the first 

 pair of pleopods were developed with a broad expanded distal 

 part just as in adult males of Polycheles. This individual had 

 also an appendix masculina in addition to an appendix interna 

 on the second pair of pleopods. Bouvier (1905 (b.)) has also 

 described an adult male measuring 35 mm., the type specimen 

 of E. spinoculatus. In one of the Helga specimens also the first 

 pleopods are well developed and of the normal male type 



