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marked ciliated spine. Natatory legs built on the very same type as in the 2 

 preceding species; inner ramus of 4th pair somewhat longer than the first 2 

 joints of the outer combined; distal joint narrowed in its outer part, with the 

 apical spines of moderate length. Last pair of legs with the free joint more 

 produced than in the other species and having the apical setae of nearly equal 

 length, none of them spiniform. Ovisacs large, oblong in form, and extending 

 far beyond the end of the tail. 



Male, as usual, smaller than female, and having the anterior division 

 of the body somewhat less broad, being moreover easily recognised by the 

 greatly inflated genital segment. Posterior rnaxillipeds powerfully developed, 

 with a dense row of delicate spinules along the inner edge of the propodos; 

 dactylus slender and abruptly curved in the middle. 



Body in both sexes semipellucid, with a violaceous or in some cases 

 orange tinge. 



Length of adult female about 1.20 mm., of male 0.90 mm. 



Remarks. -This form was described as early as the year 1853 by 

 Leydig under the name of Doridicola agi/is. It has subsequently been observed 

 by several authors, and recorded under different names. In the year 1862 my 

 late father described it as a new form under the name Eolidicola tenax, being 

 unaware of Leydig's paper, and Glaus, who found that Leydig's species ought 

 to be referred to Thorell's genus Lichomolgus, recorded it as L. doridicola. 

 The specific name agilis, originally given to this form by Leydig, must how- 

 ever be retained, and this has also been done by Canu. The L. concinnits of 

 Scott is unquestionably identical with the present species. 



It is a very distinct and easily recognisable form, being especially 

 distinguished by the very broad anterior division of the body, the com- 

 paratively short tail, and the unusually powerful posterior antenna?. 



Occurrence. I have met with this form in several places, both on the 

 south and west coasts of Norway, and in most cases I have been enabled to 

 prove its parasitism on various nudibranchiate Mollusca, for instance Doris, 

 Eolis, Polycera. By other authors it has also been found on species belonging 

 to the genera Doto and Antiopa. 



Distribution. Bohuslan (Aurivillius), British Isles (Scott), coast of France 

 (Canu), Mediterranean (Glaus). 



