ERIK A : SON STENSIO 
Of the bones of the lower jaw only the mixicoronoid («splenial») ( Mco , text fig. 66; 
PI. 2 3 , fig. i) is preserved in the material of B. mougeoti so far found. This bone is very 
long and seems to have been strickingly low. It probably covered the medial side of 
the Meckelian cartilage throughout the whole length. Its most posterior part, which 
was situated about medially of the insertion of musculus adductor mandibulae, is some¬ 
what lower than the incomparably longer part in front. The anterior part is otherwise 
very distinctly differentiated from the posterior part by its tooth-bearing labial margin. 
Some large teeth embedded in stone just laterally of 
the mixicoronoid show that the dental had its normal posi¬ 
tion. The dental itself is, however, completely weathered 
away. 
Nothing is preserved of the hyoid arch and the fifth 
branchial arch. The four remaining branchial arches (text 
figs. 65, 66; PI. 23 , figs. 1, 2), on the other hand, are fairly 
complete. They are all long- and slender and are ossified to 
a considerable extend. Thus in the three most anterior 
pairs of them one finds the hypo-, cerato- and epibrancials 
occupied by ossifications, and in addition the second pair 
has an ossification in the infrapharyngobranchial. In the 
fourth pair only a ceratobranchial ossification is preserved, 
and it is uncertain whether an epibranchial ossification was 
also developed. The different ossifications in each arch were 
connected with one another by means of cartilag-inous epi¬ 
physes. 
The hypobranchials I—III (. Hbri—Hbr 3 text fig. 66; 
PI. 23 , fig. 1) are embedded in the stone in such a way that 
they are only accessible for investigation from the ventral 
side. They grow narrow towards the ventral ends, which 
are distinctly bent in a medial direction towards the copulae. 
Towards the posterior end of its anterior third hypobran- 
chial II has a small process (pr. int, text fig. 66; PI. 23 , 
fig. 1), which may either have been developed in connection 
with the insertion for the ligamentum interarcuale ventrale 
(cf. Allis 1897a, PI. XXXIII, figs. 49, 50) or may represent 
a broken ventro-medially pointing process which has been 
attached to the copuale, i. e. the anterior end of the hypobranchial II would, if the latter 
alternative were correct, have been befurcated. It is impossible to decide whether hypo¬ 
branchials I and III had similar processes. Hypobranchial IV must have been cartila¬ 
ginous if it was present as in independent segment. 
Ceratobranchials I—IV ( Cbrj — Cbr 4 , text fig. 66) are long and slender, each with a 
rather deep longitudinal furrow on the posterior surface. 
Epibranchials I—III ( Ebri — Ebr 3 , text fig. 65) are in the same way as the cerato¬ 
branchials long and slender and have on the posterior surface a relatively deep longi¬ 
tudinal furrow. The dorsal side of those of branchial arches I and II is divided by a 
Text fig. 65. 
Birgeria mougeoti Agassiz. 
Parasphenoid and parts of the visceral 
skeleton, seen from the dorsal side. 
After P. ip. 3 / t . 
Ei>r,-Efer 3) epibranchialsofthegill-arches 
I-1II; Ecpt, ectopterygoid; Enpt, ento- 
pterygoid; Ifbr 2 , infrapharyngobranchial 
belonging to gill-arch II; ,4v, maxillary; 
Psph, parasphenoid, incompletely pre¬ 
served. 
