5 I 8 Memoir Sears Foundation for Marine Research 



separately to mouth region and to lower surface of snout or a joint trunk bifurcating 

 into a corresponding oral branch and an angular branch. Jugular and oral canals ending 

 blind, but cranials, orbitals and angulars of the two sides joining to form a complex 

 closed pattern on lower anterior surface of snout." 



Claspers of males arising from axils of pelvic fins, free for their entire length; more 

 or less roughened with small denticles either along entire clasper or only at tips;'^ simple 

 rods in some, bifid in others, or with one of the branches again subdivided (trifid) in 

 still others. Prepelvic tenacula short, blade-like, either serrate along anterior margin or 

 armed with denticles on sides, each normally retracted into a dermal pocket close in 

 front of the respective pelvic fin but protruded during sexual activity. Females of some, 

 as well as males, with prepelvic pockets but no tenacula (p. 558). Frontal tenaculum 

 short, curved, club-shaped, with more or less swollen tip, armed anteriorly with stout 

 thorn-like denticles on lower side; carried pressed downward and forward into a groove 

 on forehead normally but raised during mating. 



In color the chimaeroids vary from silvery (variously marked with stripes or spots) 

 to uniform leaden or almost black, a range of coloration correlated, it seems, with the 

 depths at which they live. Some are described as faintly luminous,!^ but no luminescent 

 organs have been found on any. 



Internal Characters. The following internal characters, supplemental to those by 

 which the subclass is defined (p. 516), are of interest. Stomach less differentiated than 

 in elasmobranchs; intestine straight, the spiral valve of only 3-3 V2 turns. Heart closely 

 resembling that of elasmobranchs; arterial cone with three rows of valves. Brain es- 

 sentially shark-like; cerebral hemispheres large, each extending forward as a slender 

 tube, the so-called olfactory peduncle with olfactory bulb at extremity; diencephalon 

 trough-shaped, thin walled, and so long that hemispheres are separated from optic 

 lobes (further in some than in others); medulla expanded on either side as a frilled — 

 so-called restiform — body; optic nerves forming a chiasma. Kidney shorter and stouter 

 than in Sharks, much longer in males than in females." Gill folds'* attached to inter- 

 branchial septa nearly to their tips, much as in elasmobranchs, but septa ending out- 

 wardly about even with tips of gill folds instead of extending outward to join skin on 

 sides of neck as in elasmobranchs. The four internal gill clefts closely crowded together, 

 each cleft bearing a gill on both anterior and posterior face;'* second to fourth gill 

 arches each with a double series of low transverse folds around inner margin; fifth gill 

 arch with one such series on anterior side; hyoid arch lacking these folds. Dermal 



11. Nomenclature of the mucous canals according to Garman (Bull. Mus. comp. Zool. Harv., Ij, 1888: pis. i, 2, 4). 



12. The denticles in Holocephali are homologous with the placoid scales of elasmobranchs, both embryologically and 

 structurally, the outer layer consisting of vitrodentine. For further account of them, see especially Dean (Chimaeroid 

 Fishes, Publ. Carneg. Instn., 32, 1906: 114-116). 



13. Whitley, Fish. Aust., i, 1940: 233. 



14. For a brief general account of the anatomy of the chimaeroids, see especially Parker and Haswell (Textb. Zool., 

 2, 1940: 222). 



15. Usually called "filaments," but this is a misnomer since this term implies a string- or thread-like structure, whereas 

 the gills actually are in the form of lamellae. 



16. Thus there is a posthyomandibular hemibranch, three holobranchs, and an anterior hemibranch on the fourth gill 

 arch, on each side. 



