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and to a great extent encompassed by the 1st segment of mesosome, subcordate in 

 form, with the frontal margin thickened and deeply insinuated in the middle. Segments 

 of mesosome only visible dorsally, very narrow, band-like, lateral parts well defined 

 on the shorter side, and each projecting into a small, knob-like prominence, those on 

 the other side inconspicuous ; coxal plates only present on the former side, very 

 small and imperfectly denned from the lateral parts. Metasome more or less 

 projecting behind, abruptly contracted and slightly tapering distally, segments well 

 defined, the last one narrow conical in form, and minutely incised on the tip. 

 Oral area wholly concealed below. Incubatory plates on the shorter side of the 

 body rather small and densely crowded together, each divided by a transversal fold 

 into 2 segments; those of the other side very large, especially the 2nd, which 

 alone forms the greater part of the boundary of the marsupium ; 5th plate on 

 this side apparently wanting. Legs more or less twisted and extended dorsally, 

 those of the larger side all obliterated except the 1st one, though slight rudiments 

 of the 3 posterior ones may always be found as 3 extremely small bifurcate 

 appendages just in the angle between the mesosome and metasome. Outer la- 

 mellae of pleopoda foliaceous, rounded oval, successively diminishing in size from 

 before backwards, those on one side much larger than on the other. — Body of 

 young female, with the incubatory plates not yet fully developed, subclavate in 

 form, anterior division, as in fully grown specimens, very asymmetrical, but having 

 all the legs distinctly developed; those of the larger side however, being, rather 

 irregularly arranged and partly folded in beneath the ventral face. — Body of 

 still younger female oblong oval in form, somewhat irregularly twisted, but having 

 all the segments very sharply defined. Cephalon freely projecting in front, and 

 rather broad. Segments of mesosome strongly vaulted above, and having the 

 lateral parts on both sides considerably produced and deflexed. Metasome not 

 abruptly contracted. Legs regular on both sides, being all folded in beneath 

 the ventral face. Inner lamellae of pleopoda larger than the outer. — Body of 

 immature female (in the 1st postlarval stage) very slender, vermiform, nearly 

 symmetrical throughout, with the cephalon semicircular, and the lateral parts of 

 the segments obtusely produced; outer lamellae of pleopoda wanting. — Adult 

 male oblong, linear, with the segments of mesosome very sharply marked off 

 from each other, metasome forming an undivided piece, broad at the base and 

 conically tapered distally. Colour of fully grown female dark brownish violet. 

 Length of female attaining 1 1 mm., that of male 3 mm. 



Memories. — This form was first described by Kr0yer in the year 1840 

 as Bopyrus abdominalis, and it was 3 years later that H. Rathke published his 

 description of Phryxus kippolytes. That these two forms are identical is 



