1904.] IX LIZARDS OF THE C4EXUS TILIQUA. 155 



these ribs l^eai- " an extraordinary i-esemblance to the so-called 

 'abdominal ribs' of other reptiles," it is particularly to be 

 regretted that the term has been used in so authoritative a 

 work as the Catalogue to which reference has been made. 



Since this confusion has been quite unnecessarily introduced, 

 it will be as well to adopt the word " parasternum," ah'eady 

 used by Fiii-biinger, Gadow, and others. The Lacertili;i are at 

 least generally supposed to be without a parastei-num, which 

 is one of the points of difference used to distinguish them 

 from the genus Sjyhenodon. The above quotation from Di-. Gadow 

 implies this genei-al view, which is more explicitly stated in the 

 ' iloyal jSTatural History'*. I can find no statement in such 

 works as that section of Bronn's ' Thier-Reich ' whicli is devoted 

 to the Lacertilia, as well as in other textbooks, to the effect that 

 a parastei'num is to be found in the Lacertilia ; and I am therefore 

 free to conclude that the knowledge of its actual occurrence is 

 at least not widely spread. 



In a brief preliminary note in ' Nature ' t I pointed out the 

 existence of a series of abdominal ribs in the Scincoid Lacertiliaii 

 Tiliqua sclncoides, and I herewith submit to the Society a more 

 detailed account of these structures (text-fig. 29, p. 156), which 

 I have not up to the present succeeded in observing in any other 

 lizard. 



The chevron bones of the abdominal-iib system are thin and 

 not always easy to see ; their slender bulk, as it appears to me, 

 fully accounts for the fact that they have been previously over- 

 looked. They are not nearly so stout, so numerous, oi- so closely 

 adpressed as these bones are in an example of Hatteria of about 

 the same size as the two specimens of Tiliqua scincoides which 

 I have examined. For these reasons the bones would very 

 readil}^ be lost in preparing skeletons of Tiliqua. The distance 

 separating the chevrons in Tiliqua is 8 mm., when the abdominal 

 muscles are gently stretched but not overstretched ; the same 

 distance in the case of the dried abdominal skeleton of Hatteria 

 was not more than 4 oi- 5 millimetres. In my specimen of Hatteria 

 there wei-e quite twenty of the chevrons ; I could not detect 

 more than seven in one of the two specimens of Tiliqua. In the 

 othei- specimen these abdominal ribs were hardly at all obvious. 

 The fact that these chevrons are quite independent of the ribs — 

 and their purely superficial position, lying as they do in the 

 ventralmost sheet of muscle of the abdominal wall — is in favour 

 of regarding them as the homologues of the abdominal ribs of 

 Hatteria. It remains, however, to be shown that they overla}) 

 the true ribs as the abdominal ribs do in Hatteria. The ribs in 

 Tiliqua after the sternum do not apparently reach so far ventrally 

 as they do in Hatteria. It might therefore conceivably be held 

 that we had here to do merely with the ventral moieties of ribs 

 which were defective laterally, and that the condition occurring 



* " Anotliei- important feature in which the Order [Squamata] differs from all the 

 preceding ones is the absence of any sj'stem of true abdominal ribs or of their 

 equivalent a plastron " (vol. v. p. 107). 



t May 5th, 1904, p. 6. 



