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Family 2.—Tylide. 
The segments of the perzeon, except the first, have the 
side-plates marked off by a distinct suture. The pleon 
consists of six segments, of which the first two are very 
short and narrow. The first antenne are small, adpressed, 
one- to two-jointed. The components of the mandibular 
Spine-row are numerous. The first maxille have three 
setee on the inner plate. The second have only one plate. 
The ‘palp’ of the maxillipeds is two-jointed. The first 
pleopods are wanting (or retain a doubtful rudiment in 
the male). The second, third, fourth, and fifth pairs are, 
according to Budde-Lund, all branchial, single-branched. 
Von Ebner, however, says :—‘ The peduncular plates of the 
branchiferous caudal appendages in 7’'ylos are not essen- 
tially different from those of other Oniscoida; they carry 
as well the branchial-operculum as the branchial-sack.’ 
Of the respiratory apparatus in this family, he remarks :— 
‘The four developed branchial-opercula all contain rami- 
fied air-cavities. These consist essentially of a sack 
enclosed between the two leaves of the branchial-oper- 
culum, which divides into a number of microscopic czecal 
tubes. Quite similarly constructed air-cavities occur also 
on the two first, often on all, of the branchial-opercula of 
other Oniscoida.. These, however, are distinguished from 
those of the Tyline, by the circumstance that it is not 
openings of the under surface of the operculum, but cross 
slits on its hinder margin, that lead to them.’ The uropods 
of the Tylide are something like those of the Valvifera, 
but here the folding doors form an operculum not over 
the pleopods but over the anal opening of the telson ; they 
carry a minute single branch, and are completely covered 
dorsally by the terminal segment of the pleon. 
Tylos, Audouin, 1825? This being the only genus 
has the characters of the family. The first verbal descrip- 
tion was printed by Audouin in his ‘ Explication sommaire 
des planches des Crustacés de l'Egypte et de la Syrie.’ 
He states that J'ylos was a manuscript name given to the 
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