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584 EDWARD PHELPS ALLIS, JR. 
and this is confirmed by his statements, in a later work (’85, p. 
13-14), that no true pharyngeal element is developed in this arch, 
and that the presence of an extrabranchial in the arch shows that 
the pharyngeal element is included in the hyomandibula. From 
these statements it is evident that the hyomandibula, both of 
the Selachii and Batoidei, must have been considered by Dohrn 
to be an epi-pharyngohyal, and as there are, according to him 
(85), two visceral arches represented in the so-called hyal arch 
of these fishes, the epi-pharyngohyals of two adjoining arches 
must have fused to form the definitive hyomandibula of the adult 
selachian. ‘This fusion of two arches here has not been gener- 
ally accepted, and there is much question as to whether the car- 
tilaginous bars of the visceral arches of living fishes chondrify 
as a single piece or as four separate elements (see Gaupp ’05); 
but that the hyomandibula of the Selachii contains the unseg- 
mented epal and pharyngeal elements of the arch has, I believe, 
always been the generally accepted opinion. 
Schauinsland, however, in 1903, came to the conclusion that 
the three pieces which form the cartilaginous bar of the hyal arch 
of Callorhynchus are ceratal, epal and pharyngeal elements, and 
that the epal element (das Epibranchiale) is certainly the homo- 
logue of the hyomandibula of ‘other selachians,’ the expression 
other selachians evidently meaning both the Selachi and the 
Batoidei. This is then a marked departure from Dohrn’s con- 
clusion, just above given, for the selachian hyomandibula would 
then be a simple epal element. Gaupp was not at that time 
(05, p. 839) inclined to accept this conclusion, and said that, in 
any event, the question needed further special investigation. 
But Luther (09, p. 13) later found a pharyngeal element as a 
distinct and separate cartilage in Stegostoma tigrinum, Mus- 
telus (probably laevis) and Galeus galeus. In Stegostoma the 
element is said to be formed by two small cartilages which lie 
postero-mesial to the upper end of the hyomandibula, in a line 
practically parallel with the pharyngeal elements of the bran- 
chial arches. They are said by Luther to be attached to each 
other by a strand of connective tissue, tc be firmly bound to the 
hyomandibula, and to help in the attachment of that cartilage to 
