ROOM III. DERMAL BONES OF THE HYL.EOSAURUS. 321 



" Now the situation which the spines in the fossil occupy, 

 is precisely that which the remains of such a dermal appen- 

 dage would have been pressed into, if the carcass of the original 

 animal had sunk down and become imbedded on its back, and 

 the serrated dorsal integument squeezed to one side." ! 



Such were the reasons which led me nearly twenty years 

 ago to ascribe these remarkable bones, then for the first time 

 made known, to the dermal system of my newly discovered 

 saurian, 



In the "Brit. Assoc. Reports," 1841, Professor Owen, 

 whilst admitting that " this ingenious suggestion carries with 

 it a high degree of probability," points out objections to this 

 hypothesis, and concludes that these singular bones are in all 

 probability abdominal ribs ; and referring to the great breadth 

 of the abdominal as compared with the vertebral ribs in the 

 Ornithorhynchus, observes that " after the close repetition in 

 the Ichthyosaurus of another of the remarkable deviations in 

 those aberrant mammals from the osteological type of their 

 class, viz. in the structure of their sternal and scapular arch, 

 the reappearance of the monotrematous modification of the 

 sternal ribs in the present extinct reptile, would not be 

 surprising. 2 



It was some years after Professor Owen's objection to my 

 views had appeared, before I obtained a fragment of a dorsal 

 spine for microscopical examination ; but that test at once 

 corroborated my original interpretation; 3 and in 1850, through 

 the liberality of Mr. Peter Fuller of Lewes, I obtained a spine 

 fifteen inches in length, with the corrugated depressed base 

 entire ; and which perfectly accords in its mode of implanta- 

 tion, as well as in its internal structure, with the dermal 

 scutes of the Hylseosaurus and other reptiles. A model of 

 this spine lies on the shelf to the right of the fossil repre- 

 sented in Lign. 66. 4 



The question, therefore, is now decided in the affirmative, 

 and we have certain proof that in its dermal system the 



1 " Geology of the South-East of England." 



2 " Report on Brit. Foss." 1841 ; p. 116. 



3 " Wonders of Geology ;" 6th edit. vol. i. p. 437. 



4 See my memoir " On a Dorsal dermal Spine of the Hylseosaurus, 

 recently discovered in the strata of Tilgate Forest." " Philos. Trana." 

 for 1850, p. 391, PL XX VII. 



Y 



