AMPHIBIANS. 75 



find in nature ; for surely, if there be such a thing as morphological " isomorphism," we have it 

 here, where the whole creature is so much like a flat-bodied Water Tortoise, and where the endo- 

 skeletal thorax-girdle as perfectly enshields this sub-reptilian creature as does the exo-skeletal 

 box its nobler relative the Chelonian. 



Example 2. Pseudis paradoxa, Wagler. 



Plate VI, fig. 7 shows part of the thorax-plates, from above, of this Anouran, also from 

 Surinam. Hyrtl's preparation was made from an adult male, and I have magnified it four 

 diameters (sixteen in superficies), to make a comparison with Pipa. 



This type comes much nearer the next (highest) group than the last ; the only thing 

 keeping it out of that group being the arrested condition of the " omosternum" (o. st.), the halves 

 of which appear to be imperfectly joined at the mid-line; certainly not segmented from the 

 prse-coracoid angle. 



The bifurcate scapula (sc.), cut away above the fenestra (sc. f.) in the figure, the long, 

 slender, grooved prse-coracoid (p. cr.), the well-ossified coracoid (cr.), and the overlapping, 

 endosteally ossified prse-epicoracoid (e. cr.), are perfectly normal ; the large, elegantly egg- 

 shaped coracoid fenestrae (cr. f.) have their apices directed almost transversely. 



c. With a perfectly developed Omosternum. 1 

 C 1. Sternum devoid of Ectosteal Bone. 

 Example 1. Acrodytes Dawdinii, Fitzinger. 



Plate VII, fig. 1, shows the parts of the Shoulder in an adult female of this Brazilian 

 species, magnified two diameters. The supra-scapula (s. sc.) is somewhat fan-shaped, but it has 

 that kind of asymmetry which obtains in the leaves of the Begonia, and some other plants, the 

 anterior margin being longer than the posterior, and concave in outline, whilst the latter is 

 convex ; the outer bone is unequal in the same manner. The upper margin is arcuate, and most 

 of the cartilage is affected by " endostosis." The scapula (sc.), prae-coracoid (p. cr.), and coracoid 

 (cr.) are typical ; the coracoid fenestra (cr. f.) is an ellipse, and the epicoracoid (e. cr.) is con- 

 tinuous with a considerable amount of prae-coracoidal partially ossified cartilage, surrounded 

 by the outer bone ; this continuous sheet of cartilage crosses its fellow, the left lying on the 

 right. 



Surmounting the anterior angles of these cartilages is a perfect " omosternum " (o. st.) : 

 it is short, spatulate, and has towards its base a deposit of endosteal bone. But the 

 true (costal) Sternum (st.) is very large, and extremely interesting morphologically, being 

 divided by " endostosis" into two equal semi-osseous halves, with a narrow line of soft cartilage 

 between and behind them. With an obtusely irregular anterior margin, and slightly concave 



The Hyrtlean Collection will supply me with several instances of this culminating group ; and 

 then I shall give an account of the development of the various parts from my own dissections of the 

 Common Frog. 



