THE ZOOLOGIST
THIRD SERIES.
Vol. II.] NOVEMBER, 1878. [No. 23. |
ON SOME PECULIARITIES IN THE ANATOMY OF
SOFT-SHELLED TURTLES.
By G.A. Stockwell, M.D.
Among the remarkable forms which, while preserving a general conformity to the typical structure, Nature has impressed upon the Vertebrates, none perhaps present greater anomalies than the order Testudinata. They have ever attracted attention, and afford rich results when they become the subject of anatomical investigation. Strange to say, while the Soft-shelled Turtles of the Old World are almost exclusively confined to those regions south of the twenty- first isothermal, the distribution of their North American repre- sentatives is exactly the opposite.
In the Upper Mississippi Valley, and throughout the Great Lake Region, even as high as Athabasca, is found Aspidonectes spinifer, Agassiz (Tryonix spinifer of Lesson), which, unlike the majority of Tortoises common to this region, presents a peculiar conformation of the paws entirely unfitting it for terrestrial loco- motion, and only suitable for swimming. Each paw possesses three toes, all more or less movable, and joined together as far as the nails by broad flexible membranes; and it is by no means certain that a fourth toe is not common, though but a rudimentary tubercle, as several specimens have been seen with this peculiarity.
The observations of the writer were begun some years since under the pupilage of Professor Sager, State Zoologist of Michigan, and confined almost exclusively to Michigan and Ontario, where,
strange to say, the above-named species is common to all the
