180 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
A tripus and a scaphiuin aie described by Eeissner but no mention is made of 
clnustra or intercalaria. The scaphiuin is a small concavo-convex ossicle -without 
ascending or condylar p'-ocesses. The tripus has a straight posterior process in 
addition to the usual anterior and articular processes. For the greater part of its 
extent each tripus is said to occupy the cavity in the first vertebra through which, 
according to Ketssner, the cranial cavity communicates with the interior of the 
osseous capsule. The posterior process of the ossicle, after traversing the “ apertura 
capsulse osseae interna superior,” gains the interior of the capsule and becomes 
connected with the air-sac. 
The relations of the sinus endoljunphaticus and atrial cavities are carefully 
described The sacculi are said to lie in two shallow depressions, separated by a 
slight median ridge on the dorsal surface of the os basilare (basioccipital), in this 
respect resembling several of the Loricaroid genera, and to be connected by a trans- 
verse ductus endolymphaticus. In the absence of figures we are not quite clear as to 
the exact relations of the sinus endolymphaticus and the atria to the anterior 
vertebrm and cranial cavity, but as far as we can make out from Reissner’s description 
they appear to occupy a Y-shaped groove on the dorsal surface of the basioccipital 
and the anterior portion of the body of the “first”' vertebra, the stem of the Y, 
which is directed forwards indicating the position of the cavum sinus imparis and the 
enclosed sinus, while the backwaidly and outwardly extending arms indicate the 
position of the two atrial cavities. In a!iy case we infer that the cavum, like the atria, 
has only a fibrous roof, and this is apparently also true of the depressions for the 
sacculi, unless indeed, the latter are freely exposed in the floor of the cranial cavity. 
The want of the usual hon}’- roof to these cavities or recesses may possibly be due, as 
we would suggest, to the failure of the exoccipitals to develop their usual horizontal 
plate-like ingrowths. 
Loricaria cataphracta and L. imdirost vis. 
Two ill-preserved examples of the.se species were also examined by Reissner (32), 
and, in all essential points affecting the structures under consideration, were found to 
be in clo.se agreement. 
The “first” vertebra is said to be connected with the second by a strongly-toothed 
suture, and the neural arches of both to possess large “processus splnosi superiores,” 
united by a serrated suture with the “os occipitale superius” (supraoccipital) in the 
median line. The “first” vertebra is provided with two peculiarly-shaped lateral 
processes, which Reissner regards as probably corresponding to modified “processus 
transversi.” Each process is slightly curved in a direction outwards and backwards, 
and at its proximal extremity enclo.ses a spherical cavity. Externally this cavity 
surfaces of the hoiiy capsules. It will follow, thci-efore, that rather more than a third of the length of 
the capsules and their enclosed air-saes must he dor.’^nd to the ribs, instead of ventrad to them, and 
probably project backwards above the ribs into the dnrso-lateral muscles. 
