1010.] The Skull of Ictops. 261 



its it is in the Centetoids, and the skull is gently constricted back of the 

 orbits. The smooth cerel)ral hemis]:)hcres (as shown by the natural cast of 

 the brain) were confined almost Avholly to the parietal segment, oidy the large 

 olfactory lobes occupying the frontal segment (as in primitive mammals 

 generally). The opposite temporal crests were considerably separated and 

 not pronounced. The zygoviata were slender, but heavier than in the 

 Erinaceida% not inclined sharply downward and forward as they are in 

 Erinaceus. There was a depression in the maxillary at the anterior root of 

 the zygoma. This is not represented in Erinaceus. The orhito-temporal 

 fossa was ovoid as in INIenotyphla, less extended antero-posteriorly than in 

 the CentetidiTe. 



In palatal aspect the skull rather suggests that of Microgale but is rela- 

 tively broader. The palate, as in Gymnura, was not fenestrated and the 

 posterior border did not, as it does in Erinaceus, terminate in a prominent 

 transverse ridge but was rounded (cf. Solenodon). Hence two of the -so- 

 called Marsupial characters of Erinaceus were absent in its Oligocene fore- 

 runner. There is, however, a postero-external palatal foramen as in 

 Marsupials, Creodonts and INIenotyphla. The basicranial region differs 

 considerably in details but not in fundamental characters from the same 

 region in Erinaceus and Gymnura. The pferygoidnl ridges of the palatine 

 and alisphenoid are single on each side, as in Centetidse so that there are 

 no ectopterygoid fossa\ The tympanic flange of the hasisphenoid appears to 

 be lacking and the large ovoid petrosal is closely appressed to the side of 

 the basioccipital {cf. Solenodon). This (if the drawing of Ictops montanus 

 be correctly interpreted) is perhaps surprising, because the Miocene Caylux- 

 otherium (Ncurogymnurus) (cf. Filhol, 18S4, pi. i), which is generally re- 

 garded as an Erinaceid and therefore as a relative of the Leptictidse, already 

 had the tympanic wing of the basis})henoid highly developed. The 

 "tympanic" process of the alisphenoid m Ictops, as in the Zalambdodonts, 

 is continuous with the postglenoid ridge of the squamosal. In Erinaceus 

 the alisphenoid portion of this ridge is present and is notched inferiorly for 

 a branch of the entocarotid (p. 247), but the squamosal portion of the post- 

 glenoid ridge is atrophied. Ictops further agrees with the Zalambdodonts 

 or rather with Solenodon in the fact that the post-glenoid and post-tympanic 

 processes are well separate (widely so in Ictops), whereas in Erinaceus these 

 two are represented by the single "post-glenoid" process, which is located 

 behind the post-glenoid foramen; the post-glenoid process in Zalambdodonts 

 lies nearer the inner border, in Ictops on the outer border, of the glenoid 

 fossa. The large tympanic fossa of Ictops is accordingly bounded anteriorly 

 by the combined alisphenoid-post-glenoid ridge. Externally it is bounded 

 by a long ridge of the squamosal corresponding to the external auditory 



