1916] Dfiitifl: The Aiiatomij of IleptaiuJuis maculatus 353 



palato-quadrate (p-q.) suspends the mandible (md.) or lower segment 

 and is itself attached to the postorbital process of the cranium by the 

 strong quadrate process (qd. p.). Anteriorly the upper segment comes 

 in contact with the cranium at the orbital process (or. p.). which, as 

 we have said, fits against the basal angle. The upper and the lower 

 segments of the first arch on the left side are connected loosely in front 

 to similar segments on the right side ; but the articulations in 

 Heptanchus maculatus, in so far as I can make out, are devoid of 

 extra cartilages like those given by White (1896, p. 58, fig. 2) for 

 Heranchus. Gadow (1888) has called attention to the simple condition 

 of the joint between the palato-quadrate and mandible in Heptanchus 

 cinereus. In the species under observation I find that the joint is 

 assentially identical with that of Heptanchus cinereus, and further 

 that the ligaments binding this joint difl'er so slightly in the two 

 species as to need no additional description. 



The slender segments making up the hyoidean or second visceral 

 arch are entirely hidden in lateral view by the first or mandibular 

 arch. The upper segment, the epihyal, unlike that in a more highly 

 specialized form as, for example Hcterodontus (Daniel, 1915), is not 

 a suspensorium for the mandibular arch. The lower and much longer 

 ceratohyal segment of the hyoid arch projects forward antl inward 

 and is connected with the eeratohyoid of the opposite side by a broad 

 basihyoid {hh., text-fig. B.) 



Both the epihyal and the ceratohyal segments are provided with 

 numerous cartilaginous rays (6.r., pi. 28, fig. 3) which support the 

 main respiratory .structures. The cartilaginous rays in this arch, due 

 to the fusion of numerous rays into a common stem, are more complex 

 than are similar rays found on the branchial arches. 



The branchial arches of right and left side form a complete ring 

 around the pharynx only with the most anterior segment. Back of 

 this, the arches unite ventrally but do not join dorsally. The first 

 branchial arch ( text-fig. A ) consists of : ( 1 ) a long slender pharyngo- 

 branchial (ph), the tip of which is joined to the arch from the oppo- 

 site side; (2) a short epibranehial (c6) ; (3) a long ceratobranchial 

 [ch) ; and (4) a relatively insignificant hypobranchial {Kb) segment. 

 Like the branchial arches in pentanchid sharks, these segments slant 

 obliquely forward and downward, roughly forming the letter S. 



In the arches following the first branchial the segments are similar 

 to those of the first, back to and including the sixth arch, with the 

 exception of the hypobranchial segments. The hypobranchials {hi), 



