230 BULLETIN OF THE 



cartilaginous consistency, in others they were soft like ordinary tissue; the 

 other end of the intestine passes over the posterior adductors firmly knitted 

 to the fascia by connective tissue and having two thin broad bands of muscle 

 parallel with it which seem adapted to give some voluntary motion to the 

 free end of the intestine, which projects 10.0 mm. beyond its attachments, near 

 its end is deeply constricted, and ends in a small round centrally pierced but- 

 ton-like expansion. The diameter of the terminal button is about 0.37, of the 

 constriction 0.25, of the internal tube about 0.25, and the average of the free 

 part of the intestine 0.5-0.7 mm. The diameter of the tube is somewhat 

 irregular, and it contained, in the specimens examined, more or less dark gray 

 fsecal matter. In the structure of the two ends of the alimentary canal this 

 mollusk resembles Trigonia and some Fectinidce. The liver presented differ- 

 ent appearances in different specimens ; in younger but pretty well developed 

 examples it presented the appearance of a number of free simple deep olive- 

 green tubules radiating from a comparatively small plexus as a centre, through 

 which passed the intestine ; in older specimens it had actj^uired a more solid 

 and compact consistency, the single tubules were no longer recognizable, the 

 interior was brownish when cut, and the outer surface was ornamented with 

 a few whitish dendritic branches extending over it from the generative glands 

 below the liver ; the mass of the ovaries or sperm glands occupy part of an 

 irregular space behind the mouth and in front of the posterior adductors, the 

 liver projects into it beneath its surface in the median line, its lower external 

 surface is keeled, but a foot is not developed; the substance of the ovary is 

 disposed in, proportionally, rather large ramifications, with acorn-shaped* 

 lobules containing granular cream-colored matter irregularly distributed on 

 the inner surface ; the supposed male gland was similar, but the contents were 

 of a finer consistency and of a more greenish color. The texture of all the 

 viscera is extremely loose and delicate, and their disposition differed in minor 

 details in all the animals examined. This might be partly owing to the vio- 

 lence necessary, even with the greatest care, to open the valves so that the 

 soft parts could be examined, and the extreme delicacy of the visceral tissues. 

 The organ of Bojanus was not distinctly recognized. The gills are of a very 

 primitive type, resembling the palpi of some Acephala in form, though not in 

 construction ; there are no true palpi ; the gills originate above the mouth 

 and behind the anterior adductor ; their bases extend backward in a nearly 

 right line to the lower surface of the posterior adductors, behind which two 

 strong bands, one to each gill, anchor the main stem of the gill to the thick- 

 ened margin of the mantle above and behind the adductors ; beyond the point 

 where these muscular bands are attached, the bases of the gills curve downward, 

 hanging free, and terminate in a point reaching to the lower posterior edge of 

 the mantle. The aforesaid bases are broad stout bands carrying each a large 

 vessel and sustained by a rather stiff (chitinous) framework, or fundamental 

 tissue. From them proceed the gill-filaments, each of which is extremely long, 



* Like the acorn without its cup. 



