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 Notidanidse is a strong point in favor of genetic relationship. 



The Heart. 



Plates XVII. and XVm. 



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 beliind 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 chordtc. The auriculo-ventricular 

 opening is furnished with a pair of valves provided with chordae tendinese. 

 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 (PI. XVIII. fig. B), the muscles lie in 

 bands [cdumnce) 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 chordae teudineae. 



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 IT. maculahis 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 Pristiurus melanos- 



