NO. 1350. NATURAL HISTORY OF THE ISOPODA— RICHARDSON. 18 



family Atscllota with the exception of the j^enus Stenasellus Dollfu.s, 

 which ha.s the first three seomeiits free and well developed; in the 

 following genera of Idoteid{\3, Stenosoma Leach, Syiiidotca Ilarger, 

 Crabyzos Spence Bate, Glyptldotea Stebbing, En^HymmemiM Richardson, 

 Erlclmmelhi Benedict, Epdys Dana: in the Sphwroniid genus Civco- 

 spliBeroma Dollfus; in the genus Anarthrura Sars, one of the Chelifera; 

 and in the Cymothoid genus Ourozeuktes Milne Edwards. The pleon 

 is also unsegmented in the males of the genera Da jus Kr0yer and 

 I^oto2>hry.vus Sars, in the females of Asjjtdophry.riis Sars, in the males 

 and females of Zonopliryxus Richardson, all belonging to the family 

 DajidiB. Pkryxus Rathke has the pleon fused in the male, as is also 

 the case with Argeia Dana, Stegophryxus Thompson, Diphphryxus 

 Richardson, Miinnidion Hansen, /*«/•«?'(/<?/« Hansen, Bathygyge Hansen, 

 Pleurocrypta Hesse, Parapcneeon Richardson, and Evgyne Ris.so, all 

 Epicarid genera. Segmentation is indicated at the sides of the pleon 

 but not on the dorsal surface in the adult female of Bopyrus Latreille 

 and Bopyrma Kossman. In the Arcturid{\3 the segments of the pleon 

 are more or less coalesced. 



The first five segments are united into one in the Spheeromidae, 

 which, together with the terminal segment, forms a biarticulate abdo- 

 men, the first segment of which usually bears suture lines at the sides 

 indicating coalescence. There are two exceptions: Sphaeromides ray- 

 mondl Dollfus, supposed by Dollfus to be an archaic form, has all 

 five segments anterior to the caudal segment free; C&ieosphxroma 

 Dollfus also dift'ers from the other Sphseromidse in having all the 

 pleonal segments fused to form a single segment. The fusion of the 

 five anterior segments into one is characteristic of the Helleriidtv?, two 

 pairs of short lateral sutures marking ofi the third from the fourth, 

 and the fourth from the fifth segments. The first five .segments 

 are also united in the females of Anthura Leach, and Cyanthura 

 Norman and Stebbing, though in the male they are partially distinct. 

 Paridotea Stebbing also has a biarticulate pleon. 



The pleon in Idotea Fabricius, CoUdotea Richardson, and Sy)mii)us 

 Richardson is made up of two short segments and a large terminal 

 segment. 



ThefamilySerolidse,the genera Edotea Guerin-Meneville, Z?w^o5eawa 

 Stebbing, Chiridotea Harger, and ChsetiUa Dana have the pleon com- 

 posed of three short segments and a terminal segment. Stenasellus 

 Dollfus also has three segments anterior to the caudal segment. 



The following genera, Cleantis Dana and Glyptonotus Eights of the 

 Idoteidfe, have a five-jointed abdomen, four short segments preceding 

 the caudal segment. This is also true of Tanalx Audouin and Milne 

 Edwards, with the exception of T. rdbustus Moore. 



In the Anthuridii> the sixth segment of the abdomen is usually dis- 

 tinct from the telson, as, for example, in Antluira- Leach, Atithelura 



