. The Cambridge natural history. Zoology. 526 FISHES small polygonal plates. All* the plates are superficially orna- mented by small stellate tubercles. The ventral armature (Fig. 315) is similar to the dorsal. A large mental plate forms the hinder marsiu of the transverse slit-like mouth, the anterior limit of which is defined by the rostral plates already mentioned. Laterally may be seen a pair of small plates (x), each perforated by a small aperture, and prob- ably indicating the position of some kind of sense-organ. Posteriorly there is a large median ventral plate, in rela- tion with a pa
. The Cambridge natural history. Zoology. 526 FISHES small polygonal plates. All* the plates are superficially orna- mented by small stellate tubercles. The ventral armature (Fig. 315) is similar to the dorsal. A large mental plate forms the hinder marsiu of the transverse slit-like mouth, the anterior limit of which is defined by the rostral plates already mentioned. Laterally may be seen a pair of small plates (x), each perforated by a small aperture, and prob- ably indicating the position of some kind of sense-organ. Posteriorly there is a large median ventral plate, in rela- tion with a pair of anterior and a pair of posterior ven- tral plates. The areas between the larger plates are filled in by numerous small polygonal plates. It is possible that there is a single external branchial aperture on each jP' ' side, near the postero-lateral angle of the shield and be- hind the posterior ventro- lateral plate. The sole repre- sentative of the family is Drepanaspis gemundenensis, from the Lower Devonian of Gemiinden in Ehenish Prussia. Large examples of this fossil must have exceeded two feet in length. Fam. 3. Psammosteidae. —To this family are referred Fia. 315.—Ventral surface of Drepanaspis certain dermal plateS OCCUr- (tail ill profile). Anterior ventre- . i r lateral plates ; , external lateral ; m, ^ng, m a more Or leSS frag- mentai plate; , mid-ventral; , pos- mentarv Condition, in the Old tero-lateral ; _'.?, posterior ventro-lateral ; _ _ i -r\ r, rostral; x, orbit or sensory plate. The P^ed Sandstone and Devonian mouth andthe supposed cloacal aperture are formations of Great Britain indicated in black. (From Traquair.) and Eussia. In their size and shape, and in their stellate tubercles, these have been com- pared to the dorsal, postero - lateral, and ventral plates of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illust
Size: 1103px × 2264px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
