18 BULLETIN OF THE 
on one side and twelve on the other. There are also four pairs of ven- 
tral roots rising nearer the median line. 
The close similarity existing between the brains of Chlamydoselachus 
and the Notidanide is a strong point in favor of genetic relationship. 
The Heart. 
Plates XVII. and XVIII. 
Departing considerably from the conventional form of heart, this genus 
presents a shape that is somewhat peculiar. Seen from below, it has a 
small subquadrangular ventricle, a large auricle, and a long bulbus arte- 
riosus. The ventricle measures nearly three quarters of an inch in 
either width or length. When filled, the auricle is subtriangular, and 
measures on each side an inch and a half. The bulbus is almost twice 
as long as the ventricle. Behind the auricle, and above and behind the 
ventricle, lies the sinus, which has a capacity that nearly equals the 
bulk of the ventricle. From it the opening into the auricle is guarded 
by a pair of valves that are without chord. The auriculo-ventricular 
opening is furnished with a pair of valves provided with chordz tendinez. 
In the ventricle the cavity or chamber is small; its outlines in longitu- 
dinal section resemble those of a pipe with a short stem, the stem being 
directed toward the left upper side and the bowl toward the bulbus. 
Along the inside of the passage (Pl. XVIII. fig. B), the muscles lie in 
bands (colwmne) loosely laid one upon another, those in the posterior 
section, or stem of the pipe, running transversely, and those of the an- 
terior section being longitudinal. 
The bulbus contains six rows of valves, or seven if we count the single 
valve nearest the ventricle as a row. Two or three of the posterior 
series have chord tendinez. 
Generally among sharks the bulbus is short, and the rows of valves 
are less numerous, ranging from two to five. Professor Owen says 
(Anat. Vert., I. 474) that Hexanchus and Heptabranchias have each four 
rows of valves. From facts that have come to my notice during this 
study I reach the conclusion that the number certainly varies among 
the species of a genus, and that it probably varies among individuals of 
a species, or even in different periods of the life of an individual speci- 
men. A young Heptabranchias pectorosus at hand has five rows. A 
large H. maculatus has only three; there are in this case, however, 
traces in the middle of the bulbus as of two rows that have become 
obsolete. Of other sharks that have been examined Pristiwrus melanos- 
