MUSEUM OF COMPARATIVE ZOOLOGY. 11 
The Basihyal (bhy) is elongate, tongue-shaped, and posteriorly, at its 
widest, is half as wide as long. Behind the more slender anterior por- 
tion, glossohyal, there is a deep excavation or hole. Behind this, be- 
tween the ends of the ceratohyals, in the proper basihyal portion, it 
becomes much thicker, bulges downward, and has a couple of longitu- 
dinal ridges near the middle. The narrower anterior portion is convex ; 
posteriorly the border is concave, and with the sides forms two angles, 
the hypohyals, which are produced to meet the first pair of cerato- 
branchials. 
The basihyal of Hexanchus is broad and short, and the hypohyals are 
not distinct. That of Heptabranchias is pointed in front and has small 
hypohyals, according to Gegenbaur. Heptabranchias maculatus, how- 
ever, I find to be nearly as in Hexanchus. The articulations in both 
these cases differ from those described above, having more resemblance 
to each other. 
The Branchial Cartilages. 
Plate IX. 
Extrabranchials are not present. 
Bastbranchials (b-br). — The jirst or anterior of the series is distinct. 
It is closely connected with the first, and loosely attached by ligament 
to the second pair of hypobranchials. The second of the series is also 
distinct, but closely joined with both second and third pairs of hypo- 
branchials. The third is fused with the corresponding pair of hypos, 
has an oblique and indistinct longitudinal division, and is closely joined 
with the fourth, which in turn is fused with the jifth. The pairs of 
hypobranchials corresponding to the last two are mere processes on their 
sides. As in other Selachia, the last of the series ends in a long spine- 
like process. In transverse section the anterior four are triangular, flat 
above, keeled beneath. 
A complete series of basibranchials in unsegmented condition would 
indicate lower rank than such as that figured by Gegenbaur (Pl. XVIII. 
fig. 1) in Heptabranchias. Excepting the last of the series, higher rank 
of a genus is apparently accompanied by reduction or loss of basibran- 
chials (see Spinax, Scyllium, Galeus, and others). 
Professor Gegenbaur’s figure of Heptabranchias is not to be taken as 
characterizing the genus, since in any of the genera there are hardly two 
species alike in respect to these cartilages. In most cases the estimate 
of the value of these and other portions of the skeleton, in connection 
