Prof. W. B. Scott — Restoration of Hijcenodon. 441 



a narrow and sack-shaped termination on the anti-sicula side. From 

 all this it follows that the left branch near its proximal part is not 

 "bilaterally symmetrical," in opposition to what Moberg believed 

 was the case in the genus Bidymograptus (Nyagrapt. fran Skane, 

 p. 346). The development of the following thecee on the left branch 

 seems to be regular. The " connecting " canal, from which, on the 

 opposite side of the sicula (right side), the right theca and common 

 canal of the right branch arise, crosses the sicula somewhat obliquely, 

 so that the right branch comes to originate somewhat nearer the 

 aperture of the sicula than does the left branch. The lines of 

 growth on the connecting canal are quite continuous with those on 

 the right branch. It appears from Fig. 3 that the connecting canal 

 is really separate from the sicula. At different foci under the 

 microscope the growth-lines of both can be seen crossing one 

 another. In the broken and ragged part of the connecting canal 

 the growth-lines of the sicula alone are shown. Also in the forms 

 preserved in relief of the anti-sicula side (Fig. 2) the " connecting " 

 canal appears, and its passage into the canal from the sicula and 

 common canal of both branches is very conspicuous. The aperture 

 of the sicula is always bent to the same quarter as the apertures 

 of the thecse of the right branch. 



DiDTMOGRAPTUS GRACILIS, Tornq. Mut. PI. XIII, Figs. 7, 8. 



This specimen has not been found transparent, but the same 

 position of relief as in Didijmograptus minutus, Mut., is shown on both 

 sides. Fig. 7, sicula side; Fig. 8, anti-sicula side. The "connecting" 

 canal is here conspicuous ; the proximal end of the sicula shows 

 a fine initial apex. 



(To be continued in our next Number.) 



H' 



II. — A Eestoratiok of Stjenodon. 



By Prof. W. B. Scott, F.G.S. 

 (PLATE XIIa.) 

 'Y^NODON is one of the genera of fossil mammals which 

 has been for a long time imperfectly known. Excellently 

 preserved skulls have been described and figured by Leidy and 

 Filhol, and some of the limb-bones and vertebra3 by De Blainville 

 and Schlosser. Material was, however, lacking for a satisfactory 

 restoration of any of the species, and the specific reference of the 

 scattered bones found has always remained more or less uncertain. 

 In the season of 1894 Mr. Hatcher had the good fortune to discover 

 in the White River beds (Oligocene) of South Dakota a number 

 of remarkably fine specimens pertaining to several species of 

 SycBnodon, which at length enable us to gain an idea of the appear- 

 ance of this most remarkable animal. 



The accompanying figure (Plate XIIa) must at once strike everyone 

 as altogether grotesque and improbable, and were it not so largely 

 drawn from the remains of a single individual found together in one 

 block of matrix, I should not venture to publish it. To this individual 



