138 Field Columbian Museum — Geology, Vol. II. 



slender ribs are spread outwardly, and were not doubled up below the 

 wing bones. They cannot be ventral ribs, since these are large and broad 

 in this species of Rhamphorhynchus, according to Zittel. 



In Pterodactylus spectabilis, as figured in the books, a number of very 

 delicate abdominal ribs are shown, as depicted by Von Meyer. " An die 

 unteren Halfte des Rumpfes kommen fiinf fadenformige Abdominalrip- 

 pen. Sie sind fadenformige, ohne sich gegen die Mitte her zu verstarken, 

 und bei ihre Lange und diinnen Beschaffenheit etwas verbogen. Die erste 

 Rippe, die langste, ergiebt 0.026."* Is it possible that the abdominal 

 and vertebral ribs have been confused in this description? 



Ventral ribs or parastemum. PI. XLI, Fig. 2. The ventral ribs were, 

 for the most part, lying in position nearly contiguous with the xiphisternal 

 process. There appear to be four pairs, the first three lying together and 

 united. The first pair is somewhat uncertainly shown, broken on the left 

 side and partly concealed on the right below the border of the sternum. 

 The second pair is very distinct. They are somewhat V-shaped, co-ossified 

 and thickened in the middle, and terminating outwardly in a slender 

 point. The third pair was in position, co-ossified with the margins of the 

 second pair, but not united in the middle. Another pair is seen by the right 

 side of the tenth vertebra, partly beneath the ulna; their whole form can- 

 not be made out, but they are wider and longer, apparently, than the third 

 pair, to which they could have had no ossific union. These ribs are all 

 thin. In the restoration it seems evident that the last pair of these ribs 

 would, approach, if not actually meet at their ends, the anterior ends of 

 the prepubic processes. I am very much inclined to believe that the 

 prepubis is really not a part of the pelvis, but rather a part of the para- 

 sternal ossifications. 



One of the best descriptions extant of the ribs of pterodactyls is that 

 of von Ammon (op. ct.): 



" Die hintersten dreizehnte Rippe stellt einen zarten Knochenstreifen 

 vor. Das untere Ende der Rippen ist verdickt und bildet ein kleines 

 Gelenkkopfchen, an welchem der obertste Theil einer Gurtelrippe der 

 Bauchwand befestigt ist. . . . Durch ihre Verbindungen [d. h. der 

 Abdominalrippen] mit den oberen Rippen bestehen also vollstandige 

 Giirtel in der Bauchwand. Es schliessen sich immer zwei Bauchrippen zu 

 einem formlichen Halbkreis zusammen. Am Vereiningungspunkte ist 

 eine mediane Verdickung vorhanden, die eine nach unten Spitz auslau- 

 fendes langes Kopfchen bildet." The ventral ribs of this pterodactyl 

 {Rhamphorhynchus longicaudatus) are very thin and simple, in contrast 

 with the broad ventral ribs of the larger forms of Rhamphorhynchus, 

 according to Zittel. 



*Paleontographica, vol. x, p. 4, 1868. 



