350 University of California Publications in Zoology [Vol. 16 



In order to determine in how far the plan is a generalized one 

 I have set myself the task of studying in detail the anatomy of 

 Heptanchus maculatus, one of the species of notidanids found along 

 the Pacific coast, and I may say summarily that most of the systems 

 compared with those, say, of Heterodontus francisci, a type geo- 

 logically old, indicate so great a generalization that Heptanchus may 

 be looked upon as an elasmobranch inheriting to a great extent the 

 features of its remote ancestors. 



It is my purpose within a short time to publish all of these studies 

 in a book dealing with the anatomy of the elasmobranch fishes, but 

 since it is desirable to give some of them at this time, these will appear 

 as a series in the publications of the University of California. 



The Endoskeleton 

 The first system which I wish to consider is the endoskeleton. This 

 in Heptanchus as in other ela.smobranchs is composed of cartilage ; 

 but in the notidanids, as Roth (1911) has shown, the cartilage is of 

 a simple type. In all of those specimens of relatively immature age 

 which I have examined of Heptanchus maculatus the cartilage is ex- 

 ceedingly soft, and over large areas it is often devoid of calcification. 

 In the more mature specimens, however, some of which have measured 

 seven to nine feet in length, a considerable amount of calcification is 

 present ; but even in these it cannot be said to be a marked feature of 

 the skeleton. 



I. AXIAL SKELETON 

 The Skull 



The skull in Heptanchus maculatus is like that of other elasmo- 

 branchs in that the capsules for the nose and ear are fused to the 

 cranium ; but this shark is unlike others in having the greatest number 

 of visceral arches, supporting buccal and branchial areas, known 

 among the elasmobranchs. 



The cranium in general shape is unlike that of Heptanchus cincrrus, 

 figured by Gegenbaur (1872) or more recently by Reynolds (1913). 

 but it is remarkably like that of Hexanchus griseus (Gegenbaur, 1872. 

 pi. 1, fig. 2). From dorsal view (pi. 27, fig. 1) the cranium is shaped 

 like a violin box, broadly pointed in front and squarish at the po.sterior 

 end. Anterior to the middle segment it is constricted and back of 

 this constriction are the heavy postorbital processes {po.o.). 



