NO. 13.50. NATURAL HISTORY OF THE ISOPODA— RICHARDSON. 7 



Mimnoj)s/s M. Sars, Paniuiunna Sars, Pleurogoniuni Sars, Nannonis- 

 CKS Sar.s, and Juo't/copc 'Suvs are exceptions, having' a six-jointed pedun- 

 cle, and Euryd'icc Leach has onl}' four joints to the peduncle of the 

 second antenna'. In Plakarthritmi Chilton the third and fourth joints 

 of the peduncle of the second antenna? are flattened to form plates. 

 Variations are found in the structure of the flagcdluni. The joints of 

 the multi-articulate flagollum are all united in one tapering joint in 

 the following genera: Si/jhduus Richardson, ErichMmeUa Benedict, 

 Cleant'is Dana, and Eusynmierus Ri(;liardson. The flagellum of the 

 lower antennae is rudimentary in both sexes in the Tanaidfe, in the 

 genus »7«7'^^s«'.s Koehler, Edotea Guerin-Meneville, Epelyn Dana, Lep- 

 tanthura Sars and Cyatlmra Norman and Stebbing; also in the males 

 of Paranthura Bate and Westwood. 



A few genera, Apseudes Leach, Stenetriuini Haswell, Janthe Boval- 

 lius, Janira Leach, Trlchopleon Beddard, Janiropsis Sars, and Crure- 

 gens Chilton are characterized by having an exopod or antennal scale, 

 movable and ciliated, attached to the peduncle of the second pair of 

 antenna. 



The inferior antennae in the Epicaridea are greatly reduced. Both 

 pairs in the females of the Entoniscidfe are transformed into lips. In 

 the Crj'ptoniscidaj they are entirely wanting. 



The antennae are of great length in many Isopods. In the genera 

 Munnopms M. Sars, Eurycope G. O. Sars, and Atxiurus Latreille they 

 attain a great development, being many times longer than the bod3^ 



The greatly elongated second antennse of the Arcturidse are supposed 

 to serve as a nursery for the 3'oung, which for some time after they 

 have left the incubator}^ pouch are found clinging to the antennae of 

 the parent. In this way thej^ are protected and are able to receive the 

 nourishment which the parent secures for them and for herself. 



■3. Mouth pa I'U. — "The upper lip usualh" forms a plate projecting 

 from the top of the oral aperture over the cutting edges of the mandi- 

 l)les, and may have an inner plate lying parallel to the outer. The 

 lower lip is bilobed, or forms two pairs of lobes, of which the inner 

 pair is much the smaller. "f' 



The maxillipeds are a pair of appendages, consisting of a basal part, 

 the protopodite, usually composed of one segment; a palp or endopo- 

 dite, with varying number of joints; an epignath or epipodite, which 

 usually consists of one article, and is aflixcd to the protopodite at its 

 external margin. In the Chelifera the epignath extends within the 

 branchial cavity; in the ^Egidic it is fused with the protopodite; in 

 PlakartJirhun Chilton it is wanting. 



There are two pairs of maxilhc. The second, posterior or outer pair 

 is three-lobed at the tip, the two outer lobes being articulated to the 

 basal segment or protopodite. In the Oniscoidea the posterior maxillse 



"Stebbing, History of Crustacea, 1893. 



