Baron Francis Nopesa, Jun. — The Origin of Mosasaurs. 119 



fact, we have strong reason to doubt — whether these valves belong 

 to one and the same individual. But it is, at any rate, noteworthy 

 that the only scutum and the only approximately entire carina in 

 this small collection should agree so nearly with the conclusions 

 derived from a study of Follicipes, for the scutum measures about 

 190 mm. and the carina about 160 mm., allowing for the probable 

 damage at the end. 



In other words, we are more likely to find in the entire capitulum 

 of this fossil that these two valves are nearly equal in length; than 

 that the carina greatly exceeds the scutum in length, as is the case 

 in the genus Scalpellum. 



So far, then, as this rough calculation goes, it bears out the view 

 expressed above that the fossil belongs to the genus Follicipes as 

 defined by Darwin in dealing with the fossil pedunculate Cirripodes. 

 For a determination of this point, however, we must await the 

 researches of those who have a larger supply of material at their 

 command. 



EXPLANATION OF PLATES IX AND X. 



Fig. 1. — The left scutum of Follicipes (?) Aucklaudicus, viewed from the outer side, 



shoAviug the form of the ' chief plate.' 

 Fig. 2. — The scutum, seen edgewise, to show the outline of the 'flange,' or much 



inflexed tergo-lateral margin, as well as the general curvature of the plate. 



«, basal margin ; J, occludent margin ; c, tergo-lateral margin; d, 'flange.' 

 Figs. 3-7. — The carina. Fig. 3, dorsal view. Fig. 4, side view. Fig. 5, the basal 



margin, seen end on, to show form of tectum. Fig. 6, the fractured 



edge, to show the curvature near the distal region. Fig. 7, transverse 



section of another specimen of smaller size, at about the level of the middle 



of the valve. 

 Fig. 8. — The rostrum, external view; a small portion of the apical region is broken 



away, but the impression (c') on the rocky matrix shows the length of the 



missing part. 

 Fig. 9. — The rostrum, side view. 



Fig. 10. — The doubtful 'latus,' broken across its lower end, external view. 

 Fig. 11. — The same, viewed from the broken end. 



V. — On the Origin of the Mosasaurs. 

 By Baron Francis Nopcsa, Jun. 



CONCERNING the origin of the Mosasaurs three altogether 

 different views exist : G. Baur regarded the Mosasaurs as 

 highly specialized aquatic Varanoids ; Boulenger is inclined to trace 

 their origin back to the Neocomian Dolichosaurs ; and Osborn, in 

 a recent paper, doubts that Varanids and Mosasaurs sprang from 

 a common stem, and regards the latter as " a very ancient offshoot 

 of the Lacertilia." Some Lacertilia found in recent years in the 

 Lower Cretaceous of Dalmatia, and not yet fully compared with 

 the Mosasaurs, will, I believe, throw fresh light on this subject. 

 Among the fossil Lacertilia found in Dalmatia two types can be 

 distinguished, namely, Dolichosaurs and Aigialosaurs, the former 

 including the genera Dolichosaurus Owen, Pontosniirus Gorjanovic- 

 Kramberger (^JFydrosaurus lesinensis, Kornh.), Acteosaurus Meyer, 

 and Adriosaiirus Seeley ; the latter, Aigialosaurus G.-Kramberger, 



