213 



segment much dilated, nearly twice as broad as it is long, the 2 succeeding 

 segments small. Caudal rami likewise of inconsiderable size, scarcely longer 

 than they are broad, and somewhat divergent; apical setae not much produced 

 and somewhat spreading- Anterior antennae scarcely more than half as long 

 as the cephalic segment, and composed of 18 joints, the 1st and 3rd of which 

 are the largest. Posterior antennae with the terminal joint comparatively small 

 and of conical form, being provided with a short lateral seta and a rather 

 feeble apical spine accompanied by 2 unequal bristles; appendicular ramus 

 almost as long as the penultimate joint and carrying on the tip 3 short bristles. 

 Siphonal tube nearly oval in form. Mandibles with the extremity quite simple, 

 without any denticles. Maxillae with the inner lobe a little shorter and stouter 

 than the outer, and carrying on the end 3 rather strong subequal and densely 

 ciliated setae; outer lobe sublinear in form and provided with 4 more slender 

 apical setae. Anterior maxlllipeds very powerful, with the terminal claw ex- 

 ceedingly strong and abruptly curved at the tip in a hook-like manner. Post- 

 erior maxillipeds of quite normal structure. Natatory legs with the inner ramus 

 in the 2 anterior pairs about equal in size to the outer, in the 2 posterior 

 pairs rather smaller; spines of outer ramus in all the pairs rather small. Last 

 pair of legs with the distal joint narrow oblong in form and provided at 

 the tip with 2 comparatively short setae and inside with a very minute bristle. 

 Ovisacs globular in form, each containing a very limited number of ova. 



Male much smaller than female, and having the anterior division of 

 the body far less tumefied. Tail comparatively more fully developed, with the 

 genital segment somewhat larger and, as a rule, containing 2 globular sper- 

 matophores, genital lappets each tipped by a long seta pointing obliquely 

 outwards. Anterior antennae more strongly built than in female and composed 

 of only 16 joints, the last 2 of which form together a very movable terminal 

 part admitting of being bent against the preceding part. 



Body in female of a more or less vivid brick-red colour, that in male 

 much paler. 



Length of adult female amounting to 0.56 mm.; that of male 0.45 mm. 



Remarks. This form, as above mentioned, was first described by T. 

 Scott as a species of the genus Dermatomyzon of Glaus, but was subsequently 

 justly removed from this genus by Giesbrecht, to form the type of his new 

 genus Scottomyzon. It is an easily recognisable form, which cannot be con- 

 founded with any of the other Ascomyzontidae. 



Occurrence. I have recently found this form parasitic on our common 

 starfish, Asterias rubens taken at Riser, south coast of Norway, as also in the 



28. Crustacea. 



