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Profs. T. W. Bridge and A. C. Haddon. [June 20, 



spicule which terminates in the fibrous wall of the neural canal, 

 between the arch of the complex vertebra and the ascending process 

 of the scaphium, near the dorso-lateral margin of the anterior portion 

 of the complex centrum, with which, however, it is in no way directly 

 attached (Cryptojpterus, C allichirous) . In a few genera (Macrones, 

 Liocassis, Pseudobag?-us, &c.) the horizontal process is prolonged 

 upwards into a vertically disposed or ascending process, which also 

 lies in the fibrous wall of the neural canal, behind and parallel to the 

 ascending process of the scaphium. In all cases where an ascending 

 process is present it lies between the paired foramina for the exit of 

 the dorsal and ventral roots of the second and third spinal nerves. 



The only variations noticed in condition of the scaphium relate to 

 the occasional absence of an ascending process. 



Claustra are invariably present, but vary greatly in size, from the 

 condition of extremely slender spicules to somewhat triangular plates 

 (Pangasius buchanani). 



The air-bladder has the same fundamental structure in all the 

 S. normales. In all cases the organ is more or less cordate in shape, 

 and is subdivided internally by a T" saa ped arrangement of a primary 

 transverse septum and a longitudinal septum into three intercom- 

 municating compartments, of which one is anterior and transversely 

 disposed, occupying the anterior third of the bladder, and two 

 posterior or lateral longitudinally arranged chambers, constituting the 

 posterior two-thirds of the bladder. The dorsal wall of the anterior 

 chamber is closely moulded to the ventral and lateral surfaces of the 

 complex and fifth centra, including the subvertebral keel which these 

 centra form, and also to the ventral surfaces of the modified trans- 

 verse processes of the fourth and fifth vertebrae. The lateral portions 

 of the anterior wall of the chamber are also partially buttressed by 

 the decurved anterior margins of the transverse processes of the 

 fourth vertebra, with or without the aid of the expanded inferior 

 processes of the post-temporals (post-temporal plates), while the 

 median portion of the wall is not infrequently supported by a sub- 

 vertebral process (Arius). The lateral compartments, on the other 

 hand, are neither invested by bone, nor are they in any way directly 

 attached to the skeleton, but lie free in the abdominal cavity. Except 

 in relation to the size of the Fish, the variations in the capacity of the 

 anterior chamber as compared with those of the lateral compartments 

 are but slight, and, as a rule, any increase or diminution in the 

 relative size of the bladder is mainly due to variations in the size of 

 the lateral chambers. With the exception of two genera (Rita and 

 Axpredo) included in this group, the capacity of the anterior chamber 

 is always much smaller than the combined capacities of the two 

 lateral chambers, and, in one of the two exceptions referred to, the 

 partial suppression of the lateral compartments is compensated by the 



