FOSSIL EGG CAPSULES OF CHIMAEROID FISHES

TO the three previously reported fossil egg capsules of chimaeroid fishes this paper adds five specimens and assigns all to Chimaerotheca, new form genus. Chimaerotheca germanica and C. besselsi are from the Jurassic of Germany; C. wyomingana, from the Upper Cretaceous of Wyoming; C. newmexicana, from the Upper Cretaceous of New Mexico; C. montanana, from the Upper Cretaceous of Montana; and C. alaskana, from the Oligocene of Alaska. LATE in 1944 I found among the specimens of fossil plants in a collection brought from Alaska by Don J. Miller, of the U. S. Geological Survey, a curious impression (pl. 38, fig. 4) on fine-grained sandstone that recalled four other baffling fossils, which I had set aside 10 years ago to await further light on their identity. On comparing the two sets of specimens I was convinced of their organic similarity and relationship and began casting about in earnest for clues leading to their correct identification. Having found all these specimens among collections of fossil plants I surmised that the collectors had assumed that they represented plants or parts of plants, probably portions of palm or cycad leaves, an idea which, as the illustrations show, is not altogether fanciful. The resemblance, however, seemed to me superficial, and, remembering the circumstance that all the fossils came from brackish-water or marine sandstone strata, I turned to the consideration of possibilities among remains of marine animals. Thus, thinking of fishes, I was reminded of a paper by Gill (1905) reporting a Cretaceous chimaeroid egg case. C. W. Gilmore, of the U. S. National Museum, after seeing my material, produced Gill's specimen (pl. 38, fig. 8) and confirmed my tentative identification. To him I am particularly indebted for further valuable help and friendly encouragement in the preparation of this paper. The living chimaeroid fishes, although somewhat sharklike in appearance and in having cartilaginous skeletons, are neither sharks nor ancestral sharks, but a divergent group that comprises about 25 species distributed among the genera Chimaera, Callorhynchus, Harriotta, and Rhinochimaera. These fishes are found in all parts of the world. Some species may be taken in shallow coastal waters, and others at abyssal depths. They range from 60 to 200 cm. in length, display delicate and varied coloration, have powerful dental plates, are omnivorous, probably live in schools, and reproduce by laying large, tough, more or less leathery, brown egg capsules, which are attached by caudal filaments to rocks or other objects. Full details, including colored illustrations, concerning the appearance and anatomy of these fishes can be found in Garman (1899; 1904; 1911) and Dean (1906; 1909; 1912). The latter investigated Chimaera colliei Bennett from the Pacific Coast of the United States, made extensive studies of its life habits and embryology, and arrived at significant conclusions pertaining to the evolution of the group. Dean's descriptions and illustrations of the egg capsules of the genera of chimaeroids are particularly enlightening in the present connection. The egg capsules of living species (see pl. 39) are dartlike to elliptic in overall outline and consist of two obvious parts-the bilaterally symmetric, tough, leathery, centrally located embryo case and a thin membrane or web of variable width that extends outward from the case in the horizontal plane dividing the case into dorsal and ventral sides. These sides, except the dorsal in Chimaera, which is keeled, are ordinarily so similar in appearance that, casually examined, they cannot be readily distinguished. For purposes of description the case may be said to have snout, trunk, and tail portions, although these regions are in reality poorly defined. It may be smooth or