158 MEMOIRS OF THE CARNEGIE MUSEUM 



of cervical ribs, we meet with three pairs of true dorsal ones, they all having large 

 costal processes, and all joining with the sternum by means of their hsemapophyses. 

 There are two pairs of pelvic ribs, the first having stunted costal processes, though 

 its hsemapophyses join with the sternum. In the last pair the unciform appendages 

 are always entirely absent, and the costal ribs do not reach the sternum. Briefly 

 then, there are seven pairs of ribs in this Darter, and this I believe to be generally 

 the arrangement in all typical Cormorants. 



Several of the authorities I have referred to above have both described and fig- 

 ured the i^elvis of an Anhinga, and the bone possesses a number of interesting char- 

 acters. Fifteen vertebrae of the spinal column fuse together to form its "sacrum." 

 The leading six of these throw out their transverse processes to coossify with the ven- 

 tral surfaces of the anterior portions of the ilia. The centra of the first three are 

 markedly compressed transversely, the first one being very deep, the next less so, 

 still less so the last. A large hsemal spine is also found on the first, which becomes 

 rudimentary on the one behind, to be entirely absent in the one next in order. 

 Two or three vertebrae throw out their processes to abut, upon either side, against 

 the ilia at points just posterior to the cotyloid rings. Posterior to these, the outer 

 extremities of the processes of the vertebrae completely fuse with the inner borders 

 of the ilia; while on either side, from the acetabulse all the way to the tail, occurs a 

 row of interapophysial foramina, a feature so characteristic of the pelves of the Cor- 

 morants. The last vertebra, though not free, is to some extent individualized, and 

 the extremities of its transverse processes may not so completely ossify with the 

 ilium on either hand, which latter bones are here drawn out into peculiarly elon- 

 gated posterior processes. Viewed upon its dorsal aspect, we are to note that the an- 

 terior portions of the ilia are much horizontally expanded, while the narrowest part 

 of the pelvis is just in front of the acetabulse, where either iliac border shows a 

 marked concavity. Thorough fusion of the internal iliac borders and the " sacral 

 crista" takes place, and not even do the usual " neural canals " or ''grooves" remain 

 open posteriorly. This is well shown in Plotus levaiUanti (PI. XXL, Fig. 1). In 

 front the iliac borders develop a raised emargination, and a strong brush of coossified 

 tendons always project directly forward from the diapophyses and neural spine of 

 the leading vertebra of the " sacrum." Passing to the post-acetabular portion we find 

 that the pelvis is broader than it is in some of the Cormorants, and we are particu- 

 larly struck with the prominent crests formed by the union of the internal iliac 

 borders and the sacrum. The neural arch and the common neural spine of the lat- 

 ter is also conspicuously raised in this part of the pelvis. This begins moderately 

 about opposite the cotyloid rings, and increases as we advance towards the tail. 



