MYZOSTOMIOA' FROM THE RED SEA, 103 



size, the lengths of the specimens measuring 8'5, 8, 8, and 5 mm. 

 respectively. 



The bodies have a maximum thickness of about 1 mm. ; owing 

 to the fact that all four specimens were contracted with the sides 

 incurved ventrally, it is impossible to give exact measurements of 

 the breadths, these, however, I estimate as varying between 3 and 

 3'5 mm, in the different individuals. 



The body-disc is rounded off anteriorly and posteiuorly ; it does 

 not terminate in a point, as in M. folium. The thick body thins 

 out gradually towaixls the edges, and has a narrow translucent 

 margin which is finely notched, giving rise to a number of incon- 

 spicuous marginal processes ending in fine points. 



The dorsal surface is smooth ; a median longitudinal elevation 

 is noticeable in three specimens, and is conspicuous only poste- 

 riorly in the region of the oviduct ; on either side are feeble 

 elevations corresponding in position to the parapodial insertions. 



Mouth and cloaca are to be seen on the ventral side, situated 

 on small papillae and both close to the extremities, in this respect 

 differing from M, nanseni, where the cloacal papilla lies at the 

 commencement of the last quarter of the body, A narrow median 

 ridge projects on the ventral surface, and marks the position of 

 the stomach and I'ectum. 



The parapodia are well developed and ax'ranged in two almost 

 parallel rows; the first pair lies close behind the mouth, but the 

 insertions of the last pair are, as in M. nanseni and M. folmni, at 

 a considerable distance from the posterior termination of the body, 

 this distance varying in the different specimens between a qua,rter 

 and a third of the total length of the animal. Each parapodium 

 is strong and, as in the two species just mentioned, consists of a 

 broad musoalar region, situated proximall}^, and of a nari"Owei' 

 distal I'egion provided with a conspicuous longitudinal groove on 

 its ventral face. 



The maJe papillse are inconspicuous and have the form of short 

 conical processes in the usual position (text-fig. 23, p, 104), At first 

 I thought that suckers were absent, and I could detect none under 

 a low magnification ; the use of a higher power of the micro- 

 scope, however, revealed up to four pairs of these structures 

 between the parapodia and close to the body-margin (text-fig, 23). 

 They are much smaller than those described by v. Graff (9) in 

 M. iianseni, and are, I think, in a vestigial condition. 



The colour-pattern of M. crosslandl is quite characteristic ; the 

 dorsal surface in the spirit specimens varies from a greenish grey 

 to a brown colour, with seven or more pairs of very narrow lighter 

 bands running transversely across the body at regular intervals. 

 I have no information as to the colour of fresh individuals. 



Among a number of young specimens of M. costatmn from 

 Ul Shubuk I found two small individuals which I take to be 

 young stages of M. crosslandi. They measure 1'25 x 1 mm. and 

 1 X '75 mm. respectively. The last pair of parapodia lies much 

 closer to the posterior extremity of the body than in the specimens 



