178 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
branous portion of the bladder could still be traced. No communication between the 
two air-sacs, or between the latter and the oesophagus, was discovered. 
Although Ramsay Wright mentions and figures a transverse ductus endolym- 
phaticus [loc. cit., Plate 9, fig. 10), no reference is made to the presence or absence 
of a sinus endolymphaticus, and in none of his figures of sections taken through 
the cavum sinus imparis is that structure represented as present. It would certainly 
he interesting to know definitely if the omission is really due to the absence of the 
sinus, for if such be the case Hypophthalmus must be included with Bagarius and 
Glyptosternuin as an additional example of the correlation of retrogressive changes in 
the air-bladder with degeneration of that portion of the internal ear which is physio- 
logically related to the bladder through the Weberian mechanism. 
Sub-Family SILURID^ PROTEROPODES. 
Group : — Hypostomatina. 
Tim only examples of this singular group that we have been able to examine were 
two badly preserved specimens of Loricaria catapliracta and Plecostomus verres, and 
a skeleton of Callichthys littoralis. We are therefore only able to confirm the general 
accuracy of Reissner’s statements with reference to these genera and to supplement 
his results on one or two more or less important points. With these exceptions the 
only other Hypostomatous Siluroid about which anything is precisely known as to 
the condition of the air-lfiadder is Rhhielcpis. 
A canthiv us hystrix.^ 
For our knowledge of the air-bladder of this Siluroid we are indebted to Rbissner’s 
valuable paper (82). The nomenclature adopted by Reissneb. is somewhat difficult 
to follow, and in giving a brief abstract of his paper we shall attempt to correlate the 
terms employed by him with those used by us so as to facilitate the comparison of 
Acanthicus with other abnormal Siluroids. 
Two egg-shaped, thin-walled, osseous capsules are found one on each side of, and 
confluent with, the “first” and “second” vertebrae.t Each cajisule is somewhat 
broader in front than behind, with a maximum width of 18 mm. and a length of 
32 mm. The two capsules occupy the entire width of the anterior portion of the 
abdominal cavity, and to a large extent superiorly they are invested by, and 
anchylosed to, the bones which form the })Osterior part of the cranial shield. The 
outer and anterior aspect of each capsule is prolonged downwards as a “ processus 
* Rhinelepis acanthicus, Cuv. and Val. 
t According to Reissnek tlie “ .second ” vertebra carries the first pair of ribs. If these structures are 
really ribs, tlie vertebi’a is either the fifth or the sixth, but if they are merely transverse processes it is 
probably the fifth. The “ first ” vertebra is, therefore, a “ complex,” and includes the first to the fourth 
vertebrae, inclusive, rvith the ])ossible addition of the fifth. 
