150 
taken at the level of the hind end of the auditory capsule. Comparison 
with figures 18, 19, 21 and 22 will suffice to explain its appearance. 
The whole series of sections, from which the above three are selec- 
ted, is thick and therefore individual sections show more than thin 
section would do. The entire Velasia head was embedded in celloidin 
and cut into serial sections with a microtome knife, each section being 
about 2 mm. thick. They were mounted unstained in balsam on 
large glass slides covered with large slips, and were of great use 
in assisting me to be certain of my dissections of the few rather 
shrunken specimens of Geotria at my disposal. 
I have provided numerous figures of the muscles of Geotria be- 
cause personally I found it at first very difficult to understand many 
of the figures of the muscles of Petromyzon supplied by P. FÜRBRINGER. 
References descriptive of the Figures, except those of Muscles, 
A, anus. A.B., anterior border of pharyngeus attached to under side of the 
posterior dorsal cartilage. A.C., auditory capsule. A.D., anterior dorsal cartilage. 
A.G.B., anterior bar of the branchial basket skeleton. A.L., anterior lateral cartilage. 
AN.C., anular cartilage. A.P., anterior pillar of the subocular arch. B.B., branchial 
basked. B.N., buccal nerve (plus skin sensory component ?). C, cushion behind 
flat tooth on dorsal process of piston cartilage. C.A.L., copulo-anulare ligament. 
C.P., cornual cartilage. C.P.T., conical tooth of piston cartilage. Cush., fleshy 
cushion, D.P.P.C., antero-dorsal process of piston cartilage. H.A., edge of at- 
tachment to funnel margin. E.Y.M., eye muscle. F.P.T., flat tooth borne on 
dorsal process of piston cartilage. G.A., gill aperture. @.C. gill cleft opening. 
G.H.E., glandular mass. G.S., gular sae. H.S.O., opening between so-called 
“ vomer” and cranial floor for passage of hypophysial sac. Hyo.Lat. “ hyomandi- 
bular” branch of lateralis. 1.8.8.P., inner series of leaf-like sensory appendages 
of funnel margin. M.C., mesenchymatous cranium. M.L., leaf-shaped sensory 
appendages on margin of buccal funnel. Mn.Lam., “mandibular” tooth-bearing 
lamina. M.V., median ventral cartilage. Ma.Lam., “ maxillary” tooth-bearing 
lamina. N, notochord. NA.AP., narial aperture. N.C., notochordal cartilage. 
O.C., olfactory capsule. O.O., olfactory organ. O.S.P., combined nervus profundus 
and ophthalmici superficiales V and VII. O.S.S.P., outer series of tentaculiform 
Sensory appendages of funnel. P, pedicle of anterior dorsal cartilage. P.C., piston 
(so-called “ lingual”) cartilage. P.Cells., pigment cells. P.D., posterior dorsal 
cartilage. P.J., cartilage investing pericardium. PI.A., pineal area. Pist.T., piston 
teeth (“lingual”). P.L., posterior lateral cartilage. P.O., spherical pad on upper 
surface of dorsal process of piston cartilage. P.P., posterior pillar of subocular arch. 
Q1, large motor nerve. @2, large sensory nerve with lateralis component. 
KR, paired glandular mass on dorsal side of head. SS, unpaired glandular mass on 
dorsal side of head. S.O., neuromast sense organs. S.O.A., subocular arch. 
S.0.L.L., neuromast sense organs of lateral line. $.P., sensory processes. S.T.P., 
styloid process. STY.C., styliform cartilage. 7, paired glandular mass on dorsal 
side of head. TU, paired glandular mass on dorsal side of head. U.I.M., muscle 
attached below to subocular arch and possibly representing the more ventral portion 
of the third dorsal myotome. V-.#., ventral extension of floore of cranium on to 
notochord. Vent.A., ventral (branchial) aorta. W, paired glandular mass on dorsal 
side of head. Y, unpaired glandular mass on dorsal side of head. Z, paired 
glandular mass on dorsal side of head. 
