KTJNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. N:0 3. 31 



testine. The right coeca do not attain the same dilatation in the antero-posterior 

 direction, but are, on the other hand, more produced dorsally, where they fill the 

 umbonal prominence. 



Summary and conclusions. Though attached by its right side the present 

 species does not exhibit any special development of the organs on the right side. 

 These are produced in a dorsal direction, it is true, but in the antero-posterior di- 

 rection they are less expanded than those of the left side. On the left side the 

 Ii ver as well as the genital coeca extend, in the middle of the body, beyond the 

 median line both in front of and behind the stomach. The left posterior dorsal 

 pallial nerve runs in such a manner as to give support to the view that the anterior 

 portions of the left liver have been subject to a depression över to the right from 

 a probably symmetrical original stage. The numerous and large liver ducts on the 

 left side also contribute to the impression of a stronger development of the left 

 moiety. It is possible that the rudiment of the left liver has been larger than the 

 right one ever since its origin. 



In Chama pellucida most of the liver ducts are present on the left side, too, 

 though this species is attached by this verv side. And further the chief part of the 

 liver is situated on the left half of the body. Arguing from this circumstance, com- 

 pared with the conditions found in the present new form, we arrive at the con- 

 clusion that in the latter the internal organization is, at least to a certain extent, 

 not inverse compared with the »normal» forms of Chama. 



Only a fevv details seem to realise more conspicuously a true reversation, 

 especially the duodenum, which, in the present Pseudochama, is turned in such a 

 direction that the narrower furrow lies to the right and the broader to the left, in 

 contrast to Ch. pellucida in which the position is reversed. Further, the anterior 

 aorta in our species has been more developed on the left, in Ch. pellucida on the 

 right side, but its mode of branching seems to be different and therefore not suit- 

 able for a comparison with respect to the symmetries. 



If the two forms are compared with regard to all the remaining character- 

 istics, we find for the most part agreements. The gills seem to be constructed ac- 

 cording to a similar scheme, though different in proportions: a less number of plicae 

 and of filaments constituting them is characteristic of P. pusilla. In the nervous 

 system the only difference is that in Ch. pellucida a more distinctly separated buccal 

 ganglion is present; but with regard to the accessory commissure between the 

 visceral connectives there is full agreement. In the genital system the openings alone 

 are somewhat dissimilar ; in Ch. pellucida they are »riisselartig in den Kiemenraum 

 vorgestiilpt» (Grieser 1913, p. 246). In both species the foot is reduced to a short 

 process, which is relatively smaller in Ch. pellucida and here still retains the anterior 

 retractors, which are even stronger than the posterior ones. The musculature is, 

 however, subject to variation in different species (ef. the following chapters), and 

 cannot be considered as a characteristic of generic validity. 



There remains only one internal organ to take into consideration: the nephri- 

 dium. And here the differences seem to be more conspicuous and fundamental. Tn 



