40 NILS HJ. ODHNER, STUDIES ON RECENT CHAM[DA"E. 



External morphology (figs. 38, 39). 



Mantle (fig. 38). The right horn-shaped umbonal process is formed exclusively 

 by the thickened mantle and does not contain any liver nor any genital coeca. The edge 

 of the mantle is smooth all round, even at the siphonal openings; the two siphonal 

 orifices occupy together nearly 1 jz (less than half) of the inferior margin; the pedal 

 slit is small and situated beneath the adductor, in front of which the margins of 

 the mantle are separated. Under the expiratory siphon there is, as mentioned below, 

 a strong siphonal fold projecting into the mantle cavity. 



The anterior adductor is somewhat shorter than the distance between the 

 upper ends of the adductors and larger than the posterior one (which is about 2 / 3 

 of the anterior in length). 



The labial palps are very short, scarcely reaching beneath the upper end of 

 the adductor and not equalling Ve of its length on the left side; on the right side 

 they are larger (about l U of the adductor) and situated somewhat higher, with their 

 apices directed backwards; both pairs are connected by means of lips. 



The falciform, laterally compressed f oot has a length of twice its breadth, and 

 is about 'A — V» of the length of the anterior adductor; the body behind the foot 

 is relatively short; a distinct though small triangulär lobe projects at a distance 

 from the base of the foot equal to the length of the foot. 



The gills are separated from each other as well as from the body and the 

 mantle, but with their ends descending within the strong siphonal fold (in the spe- 

 cimen shown in the figure the gills are contracted) that projects from the under 

 and lateral sides of the expiratory orifice. In the two gills the upper margins of 

 the reflected plates are quite separate from body and mantle. In the adult specimen 

 the anterior margin of the gills is somewhat retracted at the mouth, so that the 

 gill does not cover the labial palp; in the young specimen, however, the posterior 

 palp is covered. 



In another specimen (fig. 39) from Tortola, 5—10 fathoms, somewhat younger 

 than the large one, the right gill had its reflected plate attached at one point only, 

 namely at the triangulär lobe; the ends of both pairs of gills reached within the 

 siphonal fold. 



Internal anatomy. 



The intestinal canal (fig. 40). Beneath the cardial aperture of the oeso- 

 phagus, which shows, in a träns verse section, a regular plication with a dorsal 

 longitudinal crest and 5—6 furrows on its sides, the principal liver canal opens into 

 the stomach. Its width is about the same as that of the stomach. It receives a 

 great number of secondary liver canals, most of them from the left; these debouch 

 higher up than the right ones (for this reason they are not visible in the figure). 

 The large liver canal emerges on the left side of the stomach, but resumés farther 



