296 MR. G. B. SOWERBY ON NEW [^V^- ^i 



The chief difference between the skulls of P. melanogaster and 

 P. anhinga, apart from the form of the occipital style, is in the 

 form of the palatine bones ; in P. anhinga these bones are rounded 

 off posteriorly, the lateral margins curving inwards gradually. In 

 P. melanogaster, on the other hand, the thin lateral wings of the 

 palatines form a right angle behind ; they are cut perfectly square. 



There are no other very salient points of difference in the skulls 

 of these two species ; in Plotus melanogaster the ridges which bound 

 the temporal fossee above are more pronounced than in P. anhinga ; 

 but possibly this is rather a difference of age than of species. 

 However, in Garrod's figure of the skull of P. anhinga, which 

 represents that of an adult bird, and has been drawn, no doubt, from 

 one of the two skulls now in my custody, the same difference is 

 apparent ; the stronger development of the occipital style in P. mela- 

 nogaster perhaps needs a stronger development of these ridges, for 

 the two together form the line of origin of the temporal muscle. 



The postorbital processes are better developed in P. anhinga than 

 in P. melanogaster ; this cannot be a question of age, for the skull of 

 P. melanogaster is that of a younger bird than that of P. anhinga. 



With regard to other parts of the skeleton, the only differences 

 that I could detect concerned the ribs and the vertebral column. 



The skeleton of Plotus anhinga has a very rudimentary rib, con- 

 sisting of a small bit of bone, not more than half an inch in length, 

 attached to about the middle of the last complete rib. This is 

 absent from the skeleton of P. melanogaster, and has certainly not 

 been lost, for that skeleton was prepared with the greatest care. 



The ossification of "Donitz's" Bridge has been mentioned by 

 Mr. Forbes. 



C). Descriptions of Seven new Species of Land- Shells from the 

 U.S. of Colombia. By. G. B. Sowerby, F.L.S., F.Z.S. 



[Eeceived March 1, 1892.] 

 (Plate XXIII.) 



BuLiMus GUENTHERi, u. sp. (Plate XXIII. figs. 7, 8.) 



Testa anguste perforata, ovata, solida, Inevis, fusca, flnmmis 

 alhidis irregulariter angulatis et iindulatis picta ; spira conica, 

 breviuscula, apice obtusiusculo ; anfraetus 4g, convexi, ultitmis 

 f longitudinis cequans, inflatus, basi rotund atus ; columella 

 fere verticalis, plica obliqua crassitiscida munita ; afertura 

 ovalis, leviter obliqua, intus griseo-fusca ; peristoma crassum, 

 reflexum, marginibus callo crassiusculo junctis. 



Long. 41, diam. maj. 26 millim. ; apertura 12 lata, 22 longa. 



Hab. U.S. of Colombia. 



This species is remarkable for the smoothness of its surface, 

 having neither granules nor striae. In form it somewhat resembles 

 B. cnrdi7ialis (Pfeiffer), while it? markings are like those of a 



