800 REPORTS ON THE STATE OF SCIENCE.—1913. 
mg), it is highly probable that the marginals of the thecophorous 
shell are also epithecal.*° 
5. The same conclusion must be drawn from the discovery by 
Volker, that marginals may be recognised in the epithecal shell of 
Dermochelys. The lateral row of larger elements in that shell (fig. 1, 
mk) takes the same position in relation to the ends of the ribs as the 
typical marginals and, though more numerous, they are much like the 
marginals of Archelon. I find n6 valid reason why these elements in 
the Leatherback should not be true marginals, especially in the light of 
the relation of the marginals and supramarginals of Archelon. 
If the marginals are epithecal elements, it is proven that such 
elements were present in the most primitive Testudinata. 
6. In this connection it is of some importance that Menger found 
how, in the living tortoise Emyda, the marginals *! develop in the 
middle layers of the cutis, whilst the ‘ thecal ’ elements (costal plates, 
neural plates, &c.) begin their development in the deepest layers of 
Fig. 6. Carapace of Proganochelys Quenstedtii Baur, dorsal view, diagrammatic ; 
about ;1, nat. size. After Fraas, 1899, p. 409, text fig. 1, from Menger (1914). 
Epithecal elements black ; thecal elements dotted. 
Mg, marginals ; Smg, supramarginals. 
the cutis and only gradually reach the more superficial ones. In 
Chelonia and Chelodina the position of the developing marginals in 
the cutis was found to be less clear, although they certainly do not 
begin in the innermost layers of the cutis as do the thecal elements. 
This concurs with our conclusion that the marginals belong to another 
more superficial layer of dermal ossifications than the costal plates and 
the other thecal elements.*? 
30 Vélker, 1913, p. 521; Hay, however, assumed that the marginals belong to 
the thecal layer. 
31 IT see no reason to doubt that these elements of Hmyda are true marginals, 
though there is a possibility that they are secondary ; compare Boulenger, 1889, 
. 237-238. 
Peo That the marginals differ from the rest of the shell was already pointed out by 
Goette (1899, p. 431-432) and Jaekel (1906, p. 62-67; 1914). Goette (and 1914 also 
Jaekel) sees in the marginal elements homologues with the mosaic-shell of Dermochelys. 
