MUSEUM OF COMPARATIVE ZOOLOGY. 9 



Muscular System. — The muscles were of a dark reddish-brown, and 

 consisted of a pair of cardinal muscles attached on each side of the notch 

 in the haamal valve, two pair of adductors in the usual position, and the 

 pedicel muscle. No others could be distinguished. 



Brachia. — There were no apophyses, and the brachia were supported 

 by membranes of a horseshoe shape attaching them to the adductor mus- 

 cles. They consisted of a single row of distant cirrhi attached to the 

 edge of a horseshoe-shaped membrane, which passed behind the mouth and 

 was broadest on each side of the mouth, and prolonged anteriorly about 

 half the length of the valves, diminishing in breadth until it terminated in 

 a point on each side. There was no loop in the literal sense of the word. 

 On the outer edge of the membrane were long, slender, distant cirrhi, 

 about ten on each side. On the inner side of the membrane were a few 

 very short cirrhi, and the series was discontinued before passing below the 

 mouth. The external cirrhi were continuous above or behind the mouth. 

 They were tubular, hyaline, and presented transverse markings at short 

 intervals, somewhat as if they were annulated. They were about .018 of 

 an inch in length. The mantle was exceedingly thin, hyaline, with a 

 plain edge, not furnished with seta?. 



Organs of Digestion. — The mouth was transverse and small, the upper 

 " lip " somewhat produced in the median line ; the stomach was straight, 

 short, bag-shaped, and a little constricted behind the mouth. Its termina- 

 tion was csecal. Around the stomach a few yellowish hepatic digitations 

 were observed. There were no other organs ; intestine, ovaries, etc., being 

 absent. The peduncle was short and slender. 



The apex of the larger valve presented a curious appearance. It was 

 not pointed, but kidney-shaped, and its consistency appeared to be some- 

 what granulated, differing from the rest of the shell in texture. The in- 

 dentation lay in the median line just above the foramen. In the middle 

 of the nucleus two well-marked pores or hyaline points, apparently perfo- 

 rations, were clearly visible. Around the edges of the nucleus the growth 

 of the shell appeared to have been rather toward a bag-shape, and this 

 gave an appearance of constriction around the edges of the nucleus. The 

 upper margin of the arch of the foramen was a short distance below this. 

 The upper part of the arch was closed by a very thin, transparent septum 

 of shelly matter. The edge of the apex of the smaller valve appeared to 

 be of the same granular texture as the nucleus, but this merged impercepti- 

 bly into the rest. There was no cardinal process, and a shallow emargina- 

 tion or notch of rounded shape completed the opening of the foramen when 

 the valves were together. The cardinal muscles were attached on each 

 side of this notch to the interior of the shell. The teeth of the hinge were 

 already well marked. 



