gaeman: the chimaeroids. 253 



Branchial Skeleton^ Plates 12, 13. 



In orencral the branchial skeleton of Chiniaeroids does not reach so great a 

 degree of perfection as that of the Flagiostome. This is especially evident in 

 the basibranchials, copulae, which in all the species of Chiniaeroids are more or 

 less undeveloped, some of them being mere lumps of cartilage in the tissues 

 attached but remotely to the hypo- and cerato-branchials. A marked con- 

 trast in these respects is to be seen on comparison of the species figured on 

 Plates 12 and 13 with such a shark as Chlamydoselachus anguineus, one of 

 the lowest of its order, possessing the greatest degree of perfection in the 

 branchial skeleton, in which basibranchials and hypobranchials are fully de- 

 veloped and intimately connected. On the other hand, the epibranchials of 

 Chimaeroids are commonly better developed than those of the Plagiostomia. 



The branchial cartilages of Rhinochimaera pacifica, Plate 12, are typical of 

 its entire group. Such differences as there are lie mainly in the inferior con- 

 nections among the copulae. With exception of the hindmost one, the basi- 

 branchial copulae are more remotely connected with the hypobranchials than is 

 the case in the sharks; they are rounded lamps or disks of cartilage which 

 do not form close articulations. In the branchial cartilages of this species, 

 Plate 12, the three copulae between the first liasibranchial and the fifth are 

 represented by two pairs of small lumps of cartilage and a larger odd one, the 

 connections of all of which are ligamentous and remote. The glossohyal is 

 wedge-shaped and does not entirely separate the basihyals, as in case of Cal- 

 lorhynchus callorhynchus, Plate 13, Figure 3 ; it differs also from that species 

 in that it is produced forward into the tongue. The hindmost copula is broad 

 anteriorly; in the posterior third it tapers to a sharp point ; it is shaped much 

 like that of species of Chimaera, Plate 13, Figures 1 and 2, and is not so nar- 

 row and slender as that of Callorhynchus on the same plate, Figure 3. Appar- 

 ently there is considerable individual variation to be considered in connection 

 with all the Chimaeroids, especially in regard to the basibranchials. The first 

 two and the last one of the copulae appear to be regularly present, but between 

 these there are a couple which in cases are present as pairs, in others as single 

 lumps. Instead of the single copular lumps present in Callorhynchus callo- 

 rhynchus, Rhinochimaera pacifica has two pairs, Chimaera monstrosa has a 

 pair and a single large shield preceded by a small pair, and Chimaera colliei 

 has a pair and a single large shield followed by a piir. while the shield or 

 lump preceding the hindmost has a pair of small cartilages in front of it and 

 another pair behind it, Plate 13, Figure 2. Among other variations obtaining 

 among the species, that of the glossohyal is noted in connection with the 

 tongue, and those of the epibranchials from elongate and narrow in Rhinochi- 

 maera, Plate 12, Figure 2, to short and broad in Callorhynchus callorhynchus, 

 Plate 13, Figure 3, are readily to be seen on examination of the mentioned 

 figures. 



