136 



s. GOTO. 



tlie anterior lialf of the atrium are comparatively short. T have ohserv- 

 ed only a few s])ines on the posterior fice of the atrium hetween the 

 uterus and the vas deferens; and these were mostly a little longer than 

 those of tlie anterior and dorsal sides. In M. fi(^iforniix (PI. \, iig. 1) 

 the genital atrium is considerably elongated in the dors(^-ventral direc- 

 tion of the body and mny be distinguished into two portions, a 

 ventnd, hn-ger portion communicating with the exterior and a 

 dorsal, narrower portion. The larger, ventral portion receives close to 

 its opening the uterus and at its dorsal end the vas deferens. The 

 narrower, dorsal portion merely extends dorsad towards the oesophagus 

 and there ends blindly, receiving no duct. The spines which are 

 generally just perceptibly shorter than those of j\[. clegaiii^ are mostly 

 confined to the anterior face of the atrium but are also jiresent on the 

 posterior f ice for a very sh'.n"t distance continuous Avitli the anterior face. 

 The wall of the atrium is raised a little around the vas deferens, making 

 it open on a blunt papilla, (Pl.V, fig. 1). In il/, camlata (PI. \, fig. 3) 

 again, the genital atrium may be distinguished into two portions, a 

 ventral which in this case is narrower, and a dorsal portion which 

 is triana'ular in saa'ittal section and whose surface is covered with 

 long, slightly recurved spines. The ventral portion receives, as in other 

 species, the uterus near its external opening ; and at its postero-dorsal 

 corner it communicates with a cup-shaped accessory cavity, into which 

 the vas deferens opens at the top of a ccnnparatively large, teat-shaped 

 papilla. In M. >i('J)(istl.^ (PI. \\, fig. 1) the main cavity of the genital 

 ati'ium proceeds obliquely forwards from its external opening, and 

 ends with a short Ijifurcation, so that it is somewhat Y-shaped. The 

 spines are long and slightly recurved, and are present along the 

 whole anterior and dorsal surfaces of the atrium; l)ut these are divided 

 into two groups separated from each other l)y a short space, in which 

 the spines are tot:dly al)sent. As in the preceding species the vas 



