NO. 1791. 



SPERM TRANSFER IN DECAPODS— ANDREWS. 



421 



The depressed area between the scales and the shelf is especially 

 hollowed out in a rounded area some 2 mm. wjde on the median line 

 under the shelf and continuing back from that ; the shelf being 3 mm. 

 wide, but overhanging only 1 mm. The posterior edge of this central 

 pit or saucer is shown as a break in the shell line in fig. 2 between the 



Fig. 1.— Part of ventral side of thorax of Peneus setiferus with bases of legs m, iv, v, 

 S, shelf; Sc, scales, forming boundaries of the simple thelycum. 



Fig. 2.— Longitudinal median section of thelycum of Peneus setiferus, ventral surface 



above. S, shelf; Sc, scale. 



shelf (S) and the scales (Sc). The depressed saucer is bounded on 

 the sides by faint ridges which tend to meet one another posteriorly 

 as the rim of the saucer, causing the above change of level in the shell 

 as seen in section. 



