The Opisthohranchiata of South Africa. 105 



side. The mandibles 1-5 mm. long, yellow in the anterior part, 

 otherwise nearly colourless (fig. 5), the hinge very pronounced 

 (figs. 5, 6). The tongue as usual ; the yellow rasp of a breadth of 

 0-37 mm., containing 12 series of plates ; in the sheath moreover 35, 

 of which the 3 hindermost were not quite developed ; thus the total 

 number of series 47. The plates very clear yellowish ; the breadth 

 of the median plates behind 0-10 mm. ; the length of the lateral ones 

 in a straight line 0-22. The median plates (fig. laa) of usual form ; 

 the anterior refolded edge with 2 (-3) denticles on each side of the 

 pointed hook, the legs not quite of the same length. The lateral 

 plates (fig. 7) also of usual form ; the pointed hook (fig. 8) showed 

 at the upper edge 12-15 denticles, of which the hindermost 4-5 

 were much stronger; the lower edge had 4-5 rather weak and 

 blunter denticles. 



The oesophagus as usual with a widening. The liver brown. 



The penis of about the common form, somewhat compressed; from 

 its end the very pointed continuation of the vas deferens projected 

 (fig. 9). 



The larvcB of the Marsenia, the Echinospira, &c., are found widely 

 spread in plankton and carried far and wide by the currents. By 

 far the most of the forms of Marsenia described as species, including 

 this form, are probably only local varieties of the Mars, persjncua, 

 which seems to be almost cosmopolitan ; I have seen such forms 

 collected by Plate on the western coast of South America (" Die 

 Opisthobranchien der Sammlung Plate," Zool. Jahrb., Supplement- 

 heft iv., 3, 1898, pp. 564-569), and others collected by Mortensen 

 near the coast of Siam (" The Danish Expedition to Siam," 1. Gas- 

 teropoda opisthobranchiata, 1902, pp. 213 (55) -214 (56) ; pi. iii., 

 figs. 13-14). 



2. Marsenia capensis, Bgh. n. sp. 



PI. IX., figs. 13-16. 



Ten individuals of this form (four of which were male) were pro- 

 cured at Cape Point with shrimp-trawl from green mud and a depth 

 of 650-700 fms. ; one more at Cape Point by American trawl from a 

 depth of 310 fms. with bottom of sand and black specks ; moreover 

 from the same locality 13 specimens from a depth of 700-800 fms. 

 with green mud bottom (6 of 8 examined were male). Three rather 

 large (2-8 (?) and 3-5 (<?) and 4 ( (^ ) cm. long) were moreover 

 caught off Lion's Head from a depth of 131, 136, 195, 204 fms. 



They were all very contracted and stiff. 



The length of the dissected individuals varied from 14-18 mm. 



