90 
W. M. TATTEESALL. 
the genera of the family before him, but drew up his definition from the descriptions 
and figures of Willemoes-Suhm (1875). He includes in the family the single type 
genus, Petalophtlialmus, Will.-Suhm, with two species— P. armiger, Will.-Suhm, and 
P. willemoesii, a new species which he founds for the reception of the female ascribed 
by Sulim to P. armiger. 
Faxon and Hansen, however, have since pointed out that the female specimen 
described by Will.-Suhm is in reality a Boreomysis, probably B. scyphops, G. 0. Sars, 
so that if this latter view of its identity be adopted, P. willemoesii becomes a synonym 
of B. scyphops. 
Czerniavsky’s definition of the family is inadequate, inasmuch as no reference is 
made therein to the remarkable characters of the carapace, and the first and second 
thoracic limbs, while the importance which is given to the supposed characters of the 
exopods of the thoracic limbs is exaggerated, the difference in development as 
compared with those of the Mysidse being very slight. 
The definition given by Holt and Tattersall, 1906 (2), may, therefore, be adopted 
with some slight alteration in the characters ascribed to the eyes, rendered necessary 
by recent discoveries. 
Examination of British specimens of Iiansenomysis fyllse (Hansen, 1887) has 
revealed the fact that eyes are, in reality, present in this species. They resemble those 
described below for the Antarctic species, except that the lappets are much reduced 
and almost obsolete. 
Further, in a new species of Petaloplithalmus, P. oculatus, recently defined by 
Illig (1906), the eyes are described as well developed, with the cornea bright brown in 
colour and distinctly facetted. 
In the amended definition of the family, therefore, the description of the eyes 
would read :— Eyes (first cephalic appendages) small, either imperfectly developed as 
lamellar or spiniform organs, without visual elements, or furnished with a distinct- 
cornea in which visual elements are clearly defined and functional. 
Genus Hansenomysis, Stebbing. 
Arctomysis, Hansen, 1887 (non Czerniavsky, 1883). 
Hansenomysis , Stebbing, 1893. 
Hansenomysis , Holt and Tattersall, 190G (1 and 2); Tattersall, 1907. 
The name Arctomysis, given to this genus by Hansen (1887), having been already 
used by Czerniavsky (1883) for an entirely different form, was changed to 
Hansenomysis by Stebbing (1893). Arctomysis Czerniavsky is itself a synonym of 
Boreomysis G. 0. Sars. 
Of the other three genera belonging to the Petalophthalmidse — Petaloplithalmus , 
Ceratomysis and Scolophthalmus, Hansenomysis comes nearest to the last. Both 
agree in having the first thoracic limbs devoid of exopods and lacking the internal 
lamelliform moral lobe, and in the presence of well-developed exopods to the second 
