FISHERY BULLETIN: VOL. 83, NO. 1 



Figure 6. — Thelycum of Sicyonia showing 

 terms used in descriptions. 



Posterior 

 thoracic ridge 



^Sternite XI 

 Sternite XII 

 iSternite XIII 

 ^Median plate 



ii^uerior component 

 Sternite XIV 



Plat^ of sternite XIV 



Figure 7. — Sicyonia disedwardsi, 9 30 mm cl, 

 Golfo de Panama, Panama. Dorsal view of sperm 

 receptacles. Scale = 1 mm. 



^'■**^ 



consisting of trilobed membranous sacs: large, 

 longitudinally disposed, mesial lobe, extending to 

 posterior margin of sternite XIV, and two small 

 anterior lobes, one directed anteriorly and the 

 other laterally; receptacles opening by transverse 

 slits at anterolateral margins of plate of sternite 

 XIV. Median plate of sternite XIII (supported by 

 buttress of sternite XII) large, triangular or 

 flask-shaped, tapering anteriorly in long, sharp 



8 



spine; plate bearing well-defined lateral constric- 

 tions setting off posterior component. Sternite XI 

 armed posteriorly with paired spines of variable 

 size. Branchial components consisting of pleu- 

 robranchia on somite IX; single arthrobranchia on 

 somite VII (lamellar rudiment; Fig. 4D-b); an- 

 terior and posterior arthrobranchiae on somites 

 VIII through XIII, anterior member of VIII very 

 small and that of XIII vestigial; and podobranchia 



