36 Cincinnati Society of Natural History. 
division of the sinus, which still receives the right anterior 
and posterior cardinals. 
In the absence of a contractile valved conus arteriosus, 
Bdellostoma and all the Cyclostomata resemble the Teleosts 
more than the Elasmobranchs. (See text figures A, B, C.) 
A, Elasmobranch. 
B, Ganoid. 
C, Teleost. 
s, sinus venosus. 
a, auricle. 
v, ventricle. 
c, conus arteriosus. 
6, bulbus arteriosus. 
7, ventral aorta. 
k, valves. 
(From Boas’s Zoology.) 
In this respect the Bdellostoma is probably not primitive, 
since in the Sharks and Ganoids there is clearly a tendency 
to a reduction in the number of the valves and the size of 
the conus.* 
Contrary to Miiller’s statement (Vergl. Anat. der Myxi- 
noiden, pp. 180), the bulbus aorte is of entirely devoid of 
muscular fibers. As in the arteries in general, there isa small 
amount of plain muscle fibers mixed with the thick layer of 
elastic fibers. The bulbus is evidently not contractile, how- 
ever, in the ordinary sense of the word. 
*It is quite possible, however, that the absence of a conus represents a condition 
more primitive than the Elasmobranch. No valved conus appears during the devel- 
opment of Petromyzon. 
24 
