MUSEUM OF COMPARATIVE ZOOLOGY. 443 



an opening appears above and behind the valvular languette. I suspect this 

 to be clue to lesion, as 1 have not found such an opening in any of the species 

 ot Cardium I have examined. In another species, C. hians (op. cit., pi. xcvi. 

 fig. 2), the septum is considerably extended forward. A beautiful new species 

 of the subgenus Lophocardium, from the coast of Lower California, has the 

 ordinary gills of Cardium well developed, with their posterior anchorage above 

 and near the siphonal septum at its origin. The thin, slightly fibrous, but no- 

 where fleshy septum, extends forward to the foot and on each side of it. In 

 this case there is no orifice above the languette, or elsewhere in the partition. 

 Doubtless an exhaustive search would find many other groups in which certain 

 members exhibit a siphonal septum, more or less completely dividing the peri- 

 pedal chamber. Until the character has become more particularly specialized 

 and permanently established, it is evident it can have but a minor value as a 

 guide to the systematise or a test of his classification. 



In those forms in which the retractor muscles of the siphons radiate in a 

 vertical plane to the shell, forming a " pallial sinus " (e. g. Poromya mac- 

 troides), the siphonal septum, whether large or small, is membranous; in those 

 without a sinus (e. g. P. granulatci), it is more or less muscular. 



Cuspidariid^e. Cuspidaria patagonica Smith. A fine specimen of this 

 species, measuring 44.0 mm. in length, and 14.0 mm. in transverse diameter 

 was dredged in about 400 fins., off Manta, Peru; other specimens were found 

 in dredgings from the whole eastern coast of South America, the western coast 

 of that continent, and northward as far as Lower California. The larger 

 specimen afforded the following notes. 



The siphonal septum, by which name I shall refer to the dividing septxim 

 of the peripedal chamber, extends forward from the proximal end of the 

 siphons to the anterior adductor. It is divisible into three areas, a longi- 

 tudinal central muscular area occupying about two thirds of the whole septum, 

 and on each side a less muscular thin and tense membranous strip, which is 

 connected with the inside of the valves and leaves the imprint on the shell 

 which would ordinarily be taken for the outline of the " pallial sinus." The 

 central muscular area is attached by a bundle of muscular fibres above each 

 adductor on each side of the median line. All four points of attachment 

 leave well marked scars on the shell. I shall show hereafter that these 

 muscles, if not homologous with, at least perform the functions of, the siphonal 

 retractors of ordinary Pelecypods, and in forms like Poromya mactroides, where, 

 the usual retractors are present, the siphonal septum is destitute of muscu- 

 larity, or possesses it only to an inferior degree. The posterior septal muscles 

 are smaller and rounder in section, more vertical in direction, and more widely 

 separated from each other, than the anterior pair. The latter are narrow and 

 elongated on their surface of insertion, and but for the separation of the valves 

 would nearly touch in the median line. The principal body of fibres on the 

 plane of the septum is longitudinally arranged, another series crosses the 

 septum in an arched manner toward its extremities, especially behind, while 

 there are indications of still smaller series of more or less radiating fibres 

 knitting the whole fabric together and to the shell. 



