NATURAL SCIENCES OF PHILADELPHIA. 35 



tion towards the extreme end of the tail. In the form I have 

 referred to A. Columbianus ? the pore was quite different from 

 this, as seen in my figure B of plate II. In this the erect portion 

 of the pore is entirely wanting, the carinated body being arched 

 regularly down to, and overhanging the foot. The longitudinal 

 gutter-like pore is, however, plainly visible. In the two specimens 

 of the form I have referred to A. Californicus, the body is also 

 arched down to, and overhangs, the foot. On the tail, corre- 

 sponding to the gutter-like pore of the last-mentioned form, there 

 was no sign of any pore, but in its place the flesh was sponge-like, 

 without the markings which are found on the neighboring por- 

 tions of the foot. It may be, therefore, that in these specimens 

 the mucous pore was contracted or closed. No doubt it exists in 

 the living animal. 



Of the internal anatomy I have examined the nervous S3'stem 

 in both A. Galifornicus and A. Columbianus ? The ganglia pre- 

 sent the usual three sets, all globular in form, and so crowded 

 together in the suboesophageal and supercesophageal as almost to 

 form a continuous chain around the buccal mass. 



In these same two forms, also, I have examined the circulatory 

 and respiratory organs. Within the respiratory cavity is a large, 

 spongy, ear-shaped organ, attached only at one point to the roof 

 of the chamber. This, I suppose to be the renal organ, surround- 

 ing, and indeed inclosing, the heart, though it is not so arranged 

 in any of the genera described by Dr. Leidy. In Avion ho7-tensis 

 he describes the nearest approach to such an arrangement. 



I have examined the digestive system of all the forms, and 

 figured that of both A. Galifornicus and Columbianus. In the 

 latter, plate II. fig. d, p, the buccal mass (1) is large and round, the 

 salivarj' glands (4) short and broad ; the stomach (5) long and 

 large, with a decided constriction at its middle, and the usual cul- 

 de-sac (6) at its extremity, at which point the biliary ducts (7, 7) 

 enter ; from this the stomach passes into the intestine (8), which 

 proceeds first forward almost to the oesophagus, thence proceeds 

 backward to the extreme rear of the general cavity of the body, 

 and again forward to below the respiratory cavity, into which it 

 penetrates upwards as the rectuhi (9), and through which it 

 passes to the anus, whose position is described above. The intes- 

 tine in its whole course winds among, and is imbedded in, the 



