210 
ON THE STRUCTURE AND CLASSIFICATION 
from tliat given l)y Professor Owen (Mes. Mamm. p. 49). The additional details 
discovered in these’ crowns are of great interest; they indicate that there was a regular 
fore-and-aft or side to side grinding motion between the molars, such as is observed in 
the Rodents or in PhaHcolomiis ; this inference is strengthened by the rudimentary 
character of the premolars, the presence of a diastema, and the transformation of 
pm* into a molar which is apparently in progress. Upper molars of this character are 
invariably opposed by homologous lower molars with the pattern of the wearing sur- 
face reversed. The mandibular series of S. ptisillus, the type specimen, present many 
points of difference : there is no diaste ma ; the premolars are erect and functional ; 
the molars are set in a straight line, they are slender and widely separate from each 
other (fig. 14; see also Mes. Mamm., PI. II., fig. 18, A) ; the series are not subequal in 
size, blit diminish in both directions from the middle molar. In ChrysocJiloris the 
in.sectivore selected by Professer Owen as most nearly approaching the Stijlodon type, 
the tricuspid upper molars are separate, they interlock with the tricuspid lower molars, 
(the pattenis being reversed) and the motion of the jaw is vertical, but in Kurtodon 
tliere arc, strictly speaking, no cusps, and the action of the jaws must have been 
cliicfly horizontal. There is thus no real homology between the Kurtodon and Chry- 
mrfdortM dentition. The separation of this genus from Stylodon ivas made before the 
complete patterns of the Stylodon molar was known; now that it is fully known it is 
clear tliat tlie two forms belong not only to distinct genera, but to distinct families. 
.\mong the mandibular specimens which have been referred to the Stylodon, and thus 
fignriHl by Profc.s.sor Owen, (for example, fig. 3, Plate III.), there may be some which 
Indong to Kurtodon. 
BOLODON, Plate IX, fig. 16. 
Since the jmblication of Professor Owen’s memoir, another specimen, from the 
Rvklcs collection, has been received in the British Museum, which supplements the 
t\ i)c siwcimen (47,735), and gives us the complete upper dentition of this very inter- 
esting genus. Through the kindness of Air. Davies and Mr. Smith Woodward, this 
new siK'cimen, which the writer found partly covered with the matrix, was fully ex- 
posed, and the important characters of the full series of true molars were brought out. • 
linlodon IS thus known from portions of two right maxillm, one of which is com- 
plete anteriorly, the other posteriorly. Fortunately they preserve the following parts 
in common, as determined by the writer: the malar portion of the zygomatic arch; 
the maxillo-preniaxillary suture, also the first, second and third premolars and first 
molars; the.se parts agree in every particular, and justify our placing the two speci- 
mens together, as is done in the figure. The question of the maxillary suture is natu- 
ral l>iery important in its bearing upon the dentition of Bolodon. Professor Owen 
h- ‘yPe speci- 
,rZ. r ™ a strong light, no doubt remained as to the 
too* P-'^e^ed. This result was eonfirmed 
t an exammation of the second specimen, in which a fracture has taken place along 
