PHOTOPHORES OF DECAPOD CRUSTACEA 345 



given by Coutiere (1905, p. 7) in his re-description of Systellaspis dehilis. This account 

 he ampHfied the following year (Coutiere, 1906, p. 4), and Kemp (1910a, p. 67) later 

 compared the positions occupied by the photophores of the two species. A detailed 

 description of the structure of the elaborate pleopod photophores of S. debilis, together 

 with some observations on the remainder of the photophores, is also due to Kemp 

 (19106, p. 643). As far as I am aware no other account of the structure of the photo- 

 phores found in this genus has appeared. 



The rare S. affinis, like S. dehilis, possesses luminous organs in considerable profusion, 

 and is of considerable interest in presenting features not found in the latter species. In 

 the following account the photophores of these two species will be described and 

 compared. 



(i) Systellaspis affinis 



The single specimen of 5. affinis which I have been able to examine was one of forty- 

 five specimens obtained by the Murray Expedition from the Zanzibar area. These 

 specimens have already been described by Dr W. T. Caiman (1939, p. 190), who 

 quotes Dr Kemp's notes on the photophores. 



My examination has given no considerable support to the view that the pigment 

 spots still visible on the first abdominal segment, at the articulation points of the 

 4th/5th and 5th/6th abdominal segments, and dorsally at the base of the telson (Caiman, 

 1939, p. 191), are truly luminous organs, aUhough their position is marked in the 

 epithelial tissues by well-defined structures. 



The known photophores correspond in position in general with those of 5. debilis. 

 On continued preservation their pigmentation, which in my specimen consisted of a 

 faint red coloration, has now disappeared, and in its absence a dense white pigmentation 

 is now apparent. It is most prominent on the ocular peduncle, the carapace margin, 

 and behind the base of the last thoracic limb, but is present in many other parts of the 

 body, where it appears to reveal the presence of photophores hitherto unrecorded. In 

 addition to the positions occupied by photophores recorded by Dr Kemp, I am able 

 to mention provisionally the following as indicated by further white opaque spots : 



Brauchiostegal ivall: three scattered spots. 



Anterior border of abdominal somite 2 : one spot. 



Anterior border of abdominal somite 3 : one spot. 



Posterior border of abdominal somite 3 : one spot. 



Pleura of abdominal somites i and 3 : two spots. 



Antenna: a fine transverse streak behind the base. 



Mxpd. I : on exopod one spot. 



Mxpd. 3 : at distal and proximal ends of dactylus one spot. 



Pleopods 1,3,4 and 5 : at base of exopod one spot. 



Uropod: at base of protopodite one complex boss-shaped photophore. 



The total number of photophores apparent on the specimen I examined would 

 appear to be in the neighbourhood of 125, although due to the fact that some of the 



