220 BULLETIN OF THE 



a bare possibility that these vessels may have been the musculo-spinal 

 branches of the segments taken into the cranium. 



To the characters which Garman has selected as of value in properly 

 placing Chlamydoselachus in the zoological system may be added : — 



1. The dorsal aorta persistent throughout the entire length of the 

 chorda, its precardiac portion of large size to the occipito-atlantal line, 

 where it is suddenly much reduced to enter the cartilaginous basis 

 cranii, through which it runs below and nearly parallel with the chorda, 

 until it reaches the pituitary region, when it rises abruptly and becomes 

 in part suprachordal, ending in a vascular plexus. 



2. The absence of a complete vascular loop surrounding each gill slit, 

 ending above in two efferent branchial arteries. Chlamydoselachus has 

 but a single efferent branchial, placed in each instance cephalad of the 

 corresponding afferent vessel, agreeing in this with the usual type of 

 structure found in embryos of other Elasmobranchs. 



There are several other characters belonging to other portions of the 

 vascular system, of equal importance with the foregoing, indicative of 

 simple organization, which we may take up at some subsequent date. 



The character supposed by MuTler to be diagnostic of the Cyclo- 

 stomes, namely, that the dorsal aorta was continued beyond the union 

 of the first pair of persisting efferent branchial arteries, and that it was 

 still further connected with the anterior portion of the cephalic circle 

 (in Myxine), is not alone peculiar to this group of fishes, but is also 

 found among several Elasmobranchs. It still remains to be seen 

 whether it is absent in all the bony fishes (including the Ganoids). If 

 so, it would serve to show that the Cyclostomes and lower Elasmo- 

 branchs have retained their vascular apparatus in a much more primi- 

 tive condition than the remaining groups. Miiller did not find any 

 trace of the precardiac aorta in Sturio, and from his description of the 

 efferent branchial system it is extremely improbable that it exists in 

 any form. 



P. S. — The substance of this paper was written out in nearly its 

 present form in the fall and winter of 1887, at which time the dis- 

 sections were made, but circumstances have delayed the publication 

 till this date. 



August 1, 1889. 



