300 MR PHILIP J. WHITE ON THE 



behind the hypo-branchial plate of the second gill arch, and is fastened to it in this posi- 

 tion. The third basi-branchial (B3), which is followed by the fourth basi-branchial (B4), 

 lies immediately behind the second. The fourth is larger than the two which precede it. 

 The second and third basi-branchials lie between the inner extremities of the third pair 

 of hypo-branchials, and the fourth basi-branchial assists in separating the inner ends of 

 the fourth pair. Behind the fourth basi-branchial, but separated from it by a short 

 interval, is the large expanded breast-plate-shaped basi-branchial cartilage (B5), which is 

 the fifth of the basi-branchial series. It is broad anteriorly, but becomes narrower as it 

 passes backwards. The fourth pair of hypo-branchials (H4) are, on the one hand, con- 

 nected with the fourth basi-branchial (B4), and on the other, with the anterior edge of 

 the fifth, and their inner ends, as they pass from one basi-branchial to the other, close 

 in a space which exists between them. The cerato-branchials (Kr5) of the fifth gill 

 arch are bound to the lateral edges of the fifth basi-branchial by connective tissue. The 

 fifth basi-branchial is followed by three, it may be by two pieces of cartilage (B6, B7, B8), 

 which are the sixth, seventh, and eighth basi-branchials. Narrow cartilages placed 

 superficially are generally seen lying across the lines of contact of the fifth and sixth and 

 the sixth and seventh basi-branchials. 



The Gill rays (PI. II. Figs. 2 and 4, ~Ry, ~Ry', R,y", R,y f "). — These are found in connec- 

 tion with all the branchial arches, and are for the most part elongated rods, but in some 

 places are represented by mere nodules of cartilage. In the four anterior branchial 

 arches the rays are connected with the epi-branchial and cerato-branchial segments, but 

 most of the rays belong to the latter. The number of the rays in the various arches 

 is small as compared with that of some other Elasmobranchs. In Laemargus I 

 found eight rays to be the average number for either side of the first gill arch, and 

 five to be that for either side of the fourth. One of the rays at or near the middle 

 of each series is larger than the others, and may be known as the central ray (%'). 

 The gill rays of the fifth gill arch are much modified (Fig. 4). On the under surface 

 of each cerato-branchial (Kr5) of this arch there is an elongated piece of cartilage (Ry") 

 which is firmly bound to it, and at the outer end of this elongated cartilage I have 

 found in several cases, but not all, small nodules of cartilage (Ry" r ), which, as Gegenbaur 

 has pointed out, occur in some other Elasmobranchs, and are to be regarded as modified 

 branchial rays. 



Extra-branchial cartilages (PI. I. Figs. 1 and 2, PI. II. Fig. 2, Ev", Ei/").—¥vom 

 their position Gegenbaur calls these the outer gill arches. There are, counting those 

 belonging to the hyoid arch, five pairs on each side of the middle line, forming a dorsal 

 and ventral series. They belong to the hyoid arch and first four branchial arches. 

 The extra-branchials are elongated rods of cartilage, expanded at their inner ends and 

 with their outer extremities pointed. Most of the gill rays are directed towards them 

 (PI. II. Fig. 2), and each of the upper extra-branchials is generally touched by one or 

 more of them, but it is seldom that any ray reaches a lower extra- branchial. The outer 

 end of each central branchial ray (Ry') lies midway between the outer extremities of a 



