Notes on the collection of Triassic fishes at Yale / by G.F. Eaton.

  • Eaton, George Francis, 1872-1949.
Date:
1903
Catalogue details

Licence: In copyright

Credit: Notes on the collection of Triassic fishes at Yale / by G.F. Eaton. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    easily distinguished from other species by the peculiar develop- ment of the scales of the anterior dorsal ridge. Dr. Woodward describes his type in the collection of the Geological Society of London as follows: “A species attaining a length of about 0*2 [m]. Trunk with a considerably arched dorsal border, the depth of the caudal pedicle more than one-third as great as the maximum depth of the abdominal region. Length of head with opercular apparatus less than the maximum depth of the trunk, and con- tained four times in the total length of the fish. Fins as in S. fultus. Scales smooth and not serrated, those of the middle of the flank in part twice as deep as broad ; dorsal ridge-scales large and conspicuous, comparatively obtuse in large specimens. ” To this may be added that the last scale of the anterior dorsal ridge has its posterior end blunt and not produced, while the scale on the ventral line immediately in front of the anal fin has its posterior end notched. The ribs are more strongly developed than in other species. Semionotus ovatus W. C. Redfield. Palceoniscus ovatus W. C. Eedfield, 1841, This Journal, vol, xli. Ischypterus ovatus Sir P. Egerton, 1850, Quart. Jour. Geol. Soc., vol. vi. Ischypterus ovatus J. S. Newberry, 1888, Mon. U. S. Geol. Surv., No. xiv. Several specimens are to be found bearing this name, but, as far as the writer can ascertain, only one, the type at Columbia University, is so well preserved as to afford specific distinction. The only character given hitherto in which this species differs from others is the greater proportionate depth of body midway between the head and dorsal fin. The type specimen, however, shows another character which will probably be found more reliable, viz., a greater number of dorsal and anal fin fulcra than is found in the other American species of this genus. S. ovatus, length 11 inches, depth 3£ inches. Position and size of fins about the same as in S. fultus. Dorsal fin fulcra 21, actually preserved. Anal fin fulcra 19, actually preserved. Apparently 5 dorsal fin fulcra originate on the dorsal line, and the 6th is equal in length to a little less than one-half the anterior margin of the fin ( Plate VI, fig. 5). There is much confusion about the localities ascribed to the American species of Semionotus. For example, the two imper- fect specimens to which Agassiz applied the name S. f ultus were found at Sunderland, Massachusetts, and specimens in the Redfield Collection, whose original labels were S. fultus, have proved to be S. tenuiceps from Massachusetts and S.