504 PEOF. EAT LANKESTEE ON THE HEARTS OF 



when traced into the ventricular cavity is found to form a considerable lobe there (A in 

 tigs. 14 and 15). This possibly is the representative of the great basilar fibro-cartilage 

 of Dipnoi, whilst the third pad is relatively small, and might be expected to disappear 

 were the larger one (A) to encroach upon it. 



I do not attach any importance to these hypothetical identifications as showing affi- 

 nities between Chimoera and the Dipnoi, but rather I must insist on the fact that there 

 is so little community of structure. 



The auricle of Chimcera is not sacculated like that of Protopterus, but has a very 

 distinct pinched-off sinus (fig. 15) which opens into the auricle by a limited slit-like 

 orifice protected by valvular folds {8av). 



It is of some interest in connexion with the development of an auricular septum in 

 this and in that animal to notice that in Chimwra the auricle is incompletely divided 

 by a septal ridge into two compartments, into one of which the sinus opens, whilst 

 from the other leads the small tricuspid auriculo-ventricular passage. 



DESCRIPTION OF THE PLATES. 



PLATE LXXXIII. 



Fig. 1. Heart of Ceratodus Forsteri, right lateral view, natural size: BA, branchial 

 arteries ; Per, remnant of pericardium ; AC, arterial cone ; Au, auricle ; 

 Vn, ventricle. 



Fig. 2. Heart of Ceratodus : the ventricle and upper limb of the arterial cone have 

 been opened and the cut edges pinned back : Sp v, spiral valve ; FC, basal 

 fibro-cartilage; other letters as in fig. 1. 



Fig. 3. The same heart further dissected, the lower limb of the conus being now 

 opened by a cut indicated by the dotted line in fig. 2. AW, auriculo-ven- 

 tricular curtain valve ; vv, situation of the small pocket valves ; other letters 

 as in figs. 1 & 2. 



Fig. 4. The same heart further dissected by a cut passing along the dotted line marked 

 in fig. 3. Lv, liver ; VC, vena cava ; other letters as in preceding figures. 



Fig. 5. Inner wall of lower limb of arterial cone spread out flat, and enlarged so as to 

 show the undescribed pocket valves. Sp. V, spiral valve. 



Fig. 6. A single valve from fig. 5, enlarged so as to show the chordae tendinese. 



Fig. 7. Diagrams of the arterial cone and its longitudinal spiral valve. A, the cone 

 itself; the upper and transverse limbs have their anterior walls removed. 

 The dotted line, ss', indicates the line of origin of the longitudinal ridge or 

 "spiral" valve. B, spiral valve oi Protopterus; the shaded border {ss') is 

 that which is attached to the wall of the conus. C, the shorter spiral valve 

 of Ceratodus ; s s', attached border. 



