952 DR. W. G. RIDEAVOOD OX THE [NoV. 28, 



branchial vessels into the circulus, and the more posterior origin 

 of the subclavian arteries. 



In Fisiularia (fig. 30) the slope of the common trunks of the 

 third and fourth efferent branchial vessels is so slight that the genus 

 might with equal propriety be classed under subgroup C 6, and the 

 fact that these common trunks do not enter exactly at the pos- 

 terior angle of the circulus cephalicus makes it difficult to uphold 

 its claim to come into group C at all. The circulus is long and 

 abruptly terminated in front. The aorta, after giving origin to the 

 coeliaco-mesenteric artery, is un symmetrical, and ruusto the left side 

 of the vertebra] centra. In Sihirus (fig. 32) the posterior angle 

 of the circulus cephalicus is uot exactly coincident with the mesial 

 ends of the common trunks of the efferent branchial vessels 3 and 

 4, as it is in Saccobranchus (fig. 31) ; and thus the form re.ally 

 occupies an intermediate position between the subgroups Cc and 

 Be, in which latter subgroup the Siluroid genus Mulapteruriis 

 (fig. 12) has already been placed. M'ith regard to Saccobranchus, 

 it has already been pointed out by Hyrtl (10. p. 306) that the first 

 branchial vessel unites with the second (which is another way of 

 stating that they both open into the circulus), the thii-d with the 

 fourth, and that the efferent vessels of the lung-sac open into the 

 fourth branchial vessel. 



FUETHEE EeMAEKS ON GrOUP D. 



In Synr/nathus (fig. 33) the dorsal aorta is not median but runs 

 slightly to the left side of the vertebral centra. The coeliaco- 

 mesenteric artery arises at the posterior angle of the circulus 

 cephalicus. From the same place arises a single vessel forking 

 posteriorly into the two subclavian arteries. Hippocampus closely 

 resembles Syngnathus, but since the openings of the third and 

 fourth efferent vessels are closer together, the genus comes under 

 the second subgroup, D b. The circulus ceplialicus, also, is less 

 elongated than in Syngnathus. In both genera, however, the front 

 of the circulus is broad and its posterior angle very acute. The 

 dorsal aorta of Hippocampus is median, and the subclavian arteries 

 arise from its sides directly, and not through the intervention of a 

 common root. In Gastrosteus the circulus cephalicus is not more 

 than twice as long as broad. The subclavian arteries arise a short 

 distance behind its posterior angle, and the coeliaco-mesenteric a 

 considerable distance behind. 



j\Jolva differs from Gadus (fig. 34) mainly in the fact that the 

 subclavian arteries arise from the circulus cephalicus farther from 

 the median line, and consequently more remote from the dorsal 

 aorta. The coeliaco-mesenteric forks close to its origin in both 

 genera, as it also does in Motella. MoteJla very closely resembles 

 Molva, and it is only the slight separation of the mesial extremities 

 of the last two branchial vessels which causes the genera to be 

 placed in separate subgroups. Gadus caUarias (G. morrhua), 

 figured by Miiller (16. pi. iii. fig. 13) and by ytannius (23. pi. v. 

 fiig. 2), does not appear to differ materially from Gadus agJeJinus, 



