512 



SCIENCE 



[N. S. Vol. XXXVIII. No. I 



DISCUSSION AND COBBESPONDENCE 



THE PELYCOSAURIAN MANDIBLE 



Ten years ago I figured and described a 

 peculiar bone in the plesiosaurian mandible, 

 lying along the teeth on the inner side and 

 meeting its mate in the symphysis. It was in 

 form and position so totally unlike the coro- 

 noid bone of other reptiles that I hesitated 

 long before calling it that. Within the past 

 few years, however. Dr. Andrews has recog- 

 nized the same bone in certain European 

 plesiosaurs, and its identity seems assured. 



Some time ago I made out with consid- 

 erable confidence a similar structure in the 

 mandible of Dimetrodon, from the Permian 

 •of Texas, but, in the absence of corroborative 

 proof, I have waited till an abundance of 

 material has confirmed beyond dispute the 

 presence of a bone in the mandible lying along 

 the teeth and reaching nearly to the sym- 

 physis. It is narrow and rather loosely at- 

 tached to the dentary, so much so that it is 

 usually macerated away and lost. It lies 

 along the alveolar border, beginning in an 

 acute point opposite the middle of the third 

 tooth, and extends apparently quite to the end 

 •of the tooth series. For most of its extent it 

 is bordered below by the splenial, which di- 

 verges from it in front opposite the posterior 

 ■end of the symphysis to enclose a V-shaped 

 tongue of the dentary. It lies closely applied 

 to the bases of the teeth, covering over the 

 .alveolar pits for the growth of new teeth. It 

 .apparently ends below the last tooth by a nar- 

 row end, but it is not improbable that it is 

 very narrowly continuous with the true coro- 

 noid, and if so is quite identical with the 

 structure in the plesiosaurs. The true coro- 

 noid lies at the summit of the coronoid emi- 

 nence, extending about two inches back of the 

 -teeth. It is covered on the outer side by the 

 dentary, and is inserted in a pit in the sur- 

 angular; it is usually lost in specimens of 

 Dimetrodon. If it is continuous with the 

 alveolar bone, as it seems to be, the connection 

 must be very narrow. I doubt not that it is 

 iomologous with the bone called epicoronoid 

 hy Watson in the Stegoeephalia, even as the 



alveolar bone is homologous with his so-called 

 coronoid. 



The splenial, hitherto undescribed in the 

 Pelycosauria, is a large element lying along 

 the lower side of the mandible, visible from 

 the outer side and entering extensively into 

 the symphysis. As I have previously stated, 

 and as reafiirmed by Watson, this symphysial 

 union of the splenial is characteristic of all 

 primitive reptiles, and evidently also, of all 

 primitive amphibians. To nearly as far as 

 its middle the splenial is bordered above on 

 the inner side by the alveolar bone already 

 described. Back of its middle it is separated 

 from that bone by the slender prolongation of 

 the prearticular, precisely as in the plesio- 

 saurs. 



This resemblance of the structure of the 

 mandible in the pelycosaurs with that of the 

 plesiosaurs has an important bearing on any 

 theory of the phylogeny of the latter group. 

 They could not have originated from any 

 forms in which the coronoid had been reduced 

 to the condition in all modern reptiles. 



Full descriptions and figures of the man- 

 dible, not only of Dimetrodon, but also of 

 various other Permian reptiles and amphib- 

 ians will be published within a year. 



S. W. WiLLISTON 



TJniveesity op Chicago, 

 August 25, 1913 



THE DISTANCE HOUSE FLIES, BLUE BOTTLES AND 

 STABLE FLIES MAT TRAVEL OVER WATER 



Little evidence exists as to how far stable ■ 

 and blue bottle flies ordinarily travel to or 

 from their feeding and breeding places. 

 House flies, it is claimed, seldom stray over 

 500 yards from their breeding places; but 

 some English observations prove that they 

 may go over a mile from an infested dump 

 to the nearest village. 



In connection with the Cleveland Anti 

 Fly Campaign, urgent requests were sent in 

 to Dr. Jean Dawson for some means of relief 

 from the plague of flies on the cribs of the 

 water works, situated a mile and a quarter, 

 five miles and six miles out in Lake Erie 

 north of the city. Being in Cleveland for a 



