OCR Text |
Show 296 MR. G. B. SOWERBY ON NEW [Apr. 5, 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 fossae 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 m y custody, the same difference is apparent; the stronger development of the occipital style in P. melanogaster 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, consisting 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. 6. Descriptions of Seven n e w Species of Land-Shells from the U.S. of Colombia. By G. B . S O W E R B Y , F.L.S., F.Z.S. [Received March 1, 1892.] (Plate XXIII.) BULIMUS GUENTHERI, n. sp. (Plate XXIII. figs. 7, 8.) Testa anguste perforata, ovata, solida, Icevis, fusca, fiammis albidis irregulariter angulatis et undulatis picta ; spira conica, breviuscula, apice obtusiusculo ; anfractus 4\, convexi, ultimus § longitudinis cequans, inflatus, basi rotundatus; columella fere verticulis, plica obliqua crassiuscula munita; apertura ovatis, 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. cardinalis (Pfeiffer), while its markings are like those of a |