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taining the anal orifice, and apparently representing a trifling rudiment of 

 the tail. 



Body in the living animal of an uniform whitish colour, with the rather 

 large ova, contained within the incubatory cavity, of same colour, but more 

 opaque. 



Length of adult female 1.10 mm. 



Male unknown. 



Remarks. The above-described peculiar form looks so very different 

 from any of the other known Copepoda, that at the first sight even its reference 

 to that order of Crustacea could be questioned. Indeed, in its outward appea- 

 rance it more resembles some kinds of mites, especially the Tardigrada. 

 On a closer examination however it is soon proved to be a true member of 

 the present division of Copepoda, its extraneous appearance being the result 

 of a close adaption to its sedentary life within Ascidians. 



Occurrence. I have found this peculiar form, often in considerable number, 

 within the branchial cavity of different kinds of Ascidians, most frequently 

 in Phallusia obliqua. It may however easily escape attention, on account of 

 its small size and inconspicuous colour. The mobility of the animal is almost 

 wholly lost and the only token of life perceptible is a slight fumbling move- 

 ment of the antennae and legs. I have carefully looked over the numerous 

 specimens collected, but have not succeeded in detecting even a single male 

 among them. 



Distribution. Coast of Bohuslan (Thorell). 



Fam. 4. Ascidicolidae. 



Remarks. This family was established by Thorell, to include his genus 

 Ascidicola, which indeed exhibits several well marked peculiarities distinguishing 

 it very conspicuously from the other Notodelphyoida. As to the relation of 

 this family to the other known families of the present division of Copepoda, 

 it is evidently more sharply defined from the preceding families than from 

 those treated of farther below, agreeing with the latter in one very essential 

 character not recognised by Thorell, viz., in the absolute absence of any true 

 incubatory cavity for the reception of the ripe ova. As the family only contains 

 a single genus, it may suffice to give the characters of the latter. 



