6 THE ELASMOBRANCH FISHES 



The paired fins of Heptanchus partake slightly of the enlargement charac- 

 teristic of the forward part of the body; the pectorals {pt., fig. 15) are large, 

 but the pel vies (ventrals, pi.) are much smaller. When considered in relation 

 to other parts of the body the pectoral and pelvic fins appear close together 

 but the distance between the two is considerable, the pelvic girdle being in the 

 region of the fortieth spinal segment. The inner margin of each pelvic fin of 

 the male is modified into a clasper, which extends backward (fig. 14). The 

 claspers, however, in the immature Heptanchus inaculatus (see p. 288. fig. 

 251b, els.) are small and inconspicuous. Between the inner margins of the 

 pelvic fins and back of their bases is the cloacal opening through which prod- 

 ucts of excretion as well as the sex cells leave the bodv. 



Fig. 15. Lateral view, Heptanchus maculatus. 



ah, anal fin ; cc, supraeranial canal ; cl., branchial clefts ; dl., dorsal fin ; h inc., hyomandib- 

 ular canal; ioc, infraorbital canal; U., lateral line; pL, pelvic fin; pt., pectoral fin; soc, 

 supraorbital canal; sp., spiracle; v.l., ventral lobe of caudal fin. 



One of the most marked characteristics of Heptanchus is a single, unpaired 

 dorsal fin (dl., fig. 15). It is from this shapely fin that we get the term noti- 

 danus (vcjtov, the back; Isapos, comely) . The notidanids include both the lieptan- 

 chid and hexanchid sharks. So far as this character is concerned it applies 

 equally as well to Chlamydoselachus. 



In Heptanchus this dorsal fin lies above and slightly back of the pelvics, 

 having a position as far posterior as that occupied by the second dorsal of 

 many Elasmobranchs. The immense size of the caudal fin is due to the unusual 

 extent of its lobes and to the width of the ventral lobe (v.l., fig. 15). In the 

 ventral lobe the anterior dermal fin rays are especially well developed. These 

 fin rays are followed by a shorter series back to a notch near the terminus of 

 the lobe, behind which the dermal rays are again longer and extend in an 

 almost horizontal direction to the tip of the tail. Between the ventral lobe and 

 the cloacal opening is the smaller anal fin (al.) . 



The ground plan of coloration in Heptanchus maculatus (fig. 13) is an al- 

 most uniform drab above and light below. Scattered over the drab background 

 is a motley pattern of spots from which comes the specific name, maculatus, 

 spotted. These spots extend over the dorsal side of the paired fins and to the 

 unpaired fins, and vary in size from minute dots to clumps of pigment larger 

 than the pupil of the eye. Over the dorsal region of the body, where the pig- 

 ment is most dense, they are less conspicuous; as growth proceeds many of 

 them become hidden in the general color pattern. 



