TRIASSIC FISHES FROM SPITZBERGEN 
3o3 
int, foramen from the arteria corotis interna; al, anterior portion of the pars lateralis of either side 
of the sphenoid; a. opt, foramen probably for the arteria optica; bp, basipterygoid process; bsph, 
portion of the pars basalis of the sphenoid between the fenestra optica and the canalis transversus; 
b, c, processes on the posterior margin of the pars lateralis of either side of the sphenoid; c. transv, 
canalis transversus; d, portion of the pars basalis of the sphenoid anterior to the fenestra optica; 
fen. bas. post, probably a remaining part of the fenestra basicranialis posterior; fen. opt, fenestra 
optica; /. hyp, fossa hypophyseos; ji, fissure probably pierced by the n. abducens; my, fossa in which 
the external rectus muscle of the eye has originated. Corresponds to an antero-lateral part of the 
middle compartment of the myodome in Ami a and Teleosts; ophth. lat, exit of the n. ophthalmicus 
lateralis; ophtli. lat. If posterior opening of the canal for r. ophthalmicus lateralis on the pars lateralis 
of the sphenoid, and ophth. lat.%, anterior opening of the same canal; pc, the basal parachordal 
plate of the sphenoid; r, dorsal opening of small canal issuing from the ophthalmicus lateralis canal 
and which has contained vessels and nerve branches to the cranial roof; v lt v,g, v 3 , y 5 , openings 
of small canals for nerves and vessels to the cranial roof; V4 foramen which has probably trans¬ 
mitted the vena cerebralis anterior. II, foramen opticum; III, foramen oculomotorii; IV, foramen 
trochlearis; V, place of exit for the n. trigeminus with the exception of r. ophthalmicus profundus. 
The n. buccalis lateralis was also transmitted at this place; Vie, external opening of the canal 
for the nervus ophthalmicus profundus or a somewhat equivalent nerve. 
Plate 22. 
Fig. 1. Birgeria mougeoti (Agassiz), the neurocranium in ventral aspect. (P. i 65 ). 
» 2 . »' » > part of the axial skeleton and the endoskeleton of the dorsal 
fin (P- i5 7 ). % 
» 3. » » ». the neurocranium (P. i 65 ) in ventral aspect with parts of the 
parasphenoid and prootico-opisthotic removed. 
» 4. Boreosomus reuterskioldi n. sp., scales (P. 116). 8 / r 
» 5. Genus et Species indet. Tooth in coronal aspect. (P. if). 3 / 2 - 
Explanation of index letters. 
Ausph, autosphenotic; Bd, basidorsal; Bo, basioccipital; Lp. lepidotrichia; Ms, baseost; Pro. 0, 
prootico-opisthotic; Ps, axonost; Psph, parasphenoid; Sph, sphenoid; etc. as in PI. 21; c. sem. ext, 
canalis semicircularis externus; c. sem. post, canalis semicircularis posterior; pi, profound lamella of 
the parasphenoid; pr. asc, processus ascendens of the parasphenoid; vl, ventral lamella of the 
supratemporo-intertemporal; vp, processus from this lamella; VII, posterior opening of the facialis 
canal; cf. also Pis. 20, 21. 
Plate 23. 
Fig. 1. Birgeria mougeoti (Agassiz), part of the visceral skeleton in ventral aspect (P. 171). 
» 2. » » » parts of the visceral skeleton with the parasphenoid in dorsal 
aspect (P. 17r). 
» 3. » * » skeleton of the ventral fins. (P. i 5 f). 
» 4. Acrorhabdus asplundi n. sp., pectoral fin (P. 173c). 
Explanation of index letters. 
Cbr 1 — Cbr4, ceratobranchials of the gill-arches I—IV; Co 1 — Co 3 , ossifications in the copular 
series; Ebrj — Ebr 3 , epibranchials of the giil-arches I—III; Ecpt, ectopterygoid; Enpt, entopterygoid; 
Hbr j — Hbr 3 , hypobranchials of the gill-arches I—III; Ifbro, ossified infrapharyngobranchial of the 
