TIIK MYUlAl'dPA IN I'lir. AISIUAMAN MlSKl'M l;i?("tl, F.MANX. 101 



Aiiteiiiial groove strongly wrinkled. Jjaleral inargiii.s strongly 

 Rwollen outside tlie antennal sockets. Antennae standing 

 close together (^ : 0.80 ni 'm apart), nioderatel}' elongate, not 

 reaching (5) or scarcely over-i-eaching ((J) the posterior mar- 

 gin of the second segment, slender, shortly pilose, tipped with 

 four sensory cones. Micrometrical measurements of joints : 

 Ist, 0.4-80 'm 111: -ind, 1.152 m/m ; 3rd, 1.280 m/m'; 4th, 

 1.2-48 m/m; 5th, 1.216 m/m ; 6th, 0.992 m/m ; 7th and Sth, 

 0.256 m/m ; total length, 6.624 m/m. 



The Tomciswary organ realises a growth so far unrecorded 

 amongst Polj-desmids ; it is to be seen as a pale yellow, 

 ti'ansverse and transparent low swelling, in the shape of a 

 ci'escent with i-ounded inner angle, located exactly behind the 

 antennal socket; in the other species, this organ is consiberably 

 smaller, dot shaped, and stands in the antennal fossa, behind 

 and close to the antennal socket. 



First segment smooth. Anterior margin straight in the 

 middle, gently arched on each side ; posterior angle rounded 

 and slightly thickened, with a marginal sulcus ; posterior 

 margin feebly excised. Keels of the second segment vei'y 

 small, wath rounded anterior angle (more rounded than in 

 other species), reaching downward far below the posterior 

 angle of the keel of first segment. The margins of thi keel 

 are somewhat iucrassate, and its surface is not so strongly 

 grooved as in A. ralithovi. 



Integuments scarcely shining, with indistinct wavy sort of 

 striae lacking orientation. Keels considerably reduced, 

 rounded anteriorly ; posterior angle i"6unded on the anterior 

 segments and gradually less prominent backwards. Suture 

 densely beset with minute longitudinal striffi. From the fifth 

 segment to the seventeenth, the metazonite show a very 

 shallow transverse impression and a thin sulcus growing fainter 

 on the sixteenth and seventeenth segments ; yet the body is 

 not flattened as in A. froyyiitfi (PI. xv., fig. 20). Pores 

 opening sideways in the keels 5, 7, 9, 10, 12, 13, 15 to 19. 

 Last segment of the usual conic shape, with as few setae as in 

 the other species. Valves globular, with no distinctly I'aised 

 margins, but with a pair of low granules tipped with seta> on 

 each valve. Anal sternite lai-ge, rounded, yellow, with a pair 

 of marariual aetse. 



