274 PROCEEDINGS OF THE ACADEMY OP 



closer to the stout Celesti than the species of the latter genus are among 

 themselves. 



4. The Gronias nigrilabris is a Silurid, which in specific characters 

 more nearly resembles the Amiurus lynx, than the latter does the A.albidus 

 and many other species of the genus. The A. lynx is found in the same 

 streams. The important generic character, the absence of eyes, is, however, 

 its constant feature (in three specimens known to naturalists, others to fisher- 

 men). 



5. The Cinclidium granulatum, a large tree toad of Brazil, resembles 

 in all its characters the Centrotelma g e og ra p h i c u m. The specific differ- 

 ences between them amount to almost nothing, but both sexes of the former 

 grow larger and are furnished with a generic peculiarity in the addition of 

 some phalanges to the thumb. 



6. The Auk Sagmatorrhina s n ckl ey i Cass, is stated* to resemble in phimage 

 and all its characters the Ceratorhyncha m o n o c e r a t a, as to be not distinguish- 

 able, even as a varietj^ from it, except by the striking generic characters. In 

 the latter a concave bone-like process rises from above the nostril, and an 

 accessory piece is found in the symphysis mandibuli, both wanting in the 

 genus Sagmatorrhina. 



7. The Oporornis agilis Baird, a North American bird of the Tanager 

 family, resembles very closely in form, color and habits, the adjacent species 

 of the adjacent genus Geothlypis. While its specific characters are thus very 

 close to Geothlypis tephrocotis, it differs in the generic feature of a longer 

 wing. By this it is associated, and properly so, with another species, 0. 

 f o rm s u s, which has the general color and habits of species of Myiodi- 

 octes (M. c a n a d e n s i s), the next related genus. 



8. The following fact I give on the authority of Prof. Leidy, who will pub- 

 lish it in his forthcoming work on the extinct mammalia of Nebraska, etc. 



Three species of Oreodon occur in the miocene strata; they are a larger, a 

 medium and a small sized species. In the Pliocene beds above them they are 

 represented by three species of Merychyus, which are in all respects known, 

 identical specifically with the three preceding. Each one may thus be said to 

 be more nearly allied to the species of the other genus than to its fellow of the 

 same genus, in specific characters. But each, on the other hand, diff"ers from 

 each in generic characters. The teeth of Merychyus are more prismatic, have 

 longer crowns and shorter roots, approaching the sheep, as Oreodon does the 

 deer.f 



9. The North American Centrarchoid, Hemioplites simulans, in specific 

 characters is most closely allied to the Enneacanthus guttatus Morris.* 

 It has however one or two distinctive specific features, but it difi'ers as to genus 

 in having one less dorsal spine and one more anal spine, characters in the direct 

 line of succession of genera to Centrarchus and Hyperistius. Now the lack 

 of one of its dorsal spines is not an uncommon variation in the Enneacanthus, 

 but the anal is never known to change. There is, however, apparently no 

 reason, as far as physical causes are concerned, why it should not tend to 

 vary as much as the dorsal. The lack of this tendency constitutes Hemio- 

 plites, a genus distinct from Enneacanthus, at the present time. 



* By Coues Monograph of Alcidee. Proc. Acad. Phila., 1868, p. 34. 



t This phenomenon suggests an explanation on the score of adaptation, which the other 

 cases do not. The existence during llie later period of a tougher material of diet, would 

 increase the rapidity of wearing of the crown of the tooth, and require a longer crown 

 and greater rapidity of protrusion. This necessitates a diminution of the basal shoulder 

 and shortening of the roots, producing the pris^matic form aforesaid. The deer browse 

 on forest foliage, which is more tender, while the C'avicornia graze the grasses, which 

 contain, as is known, a greater amount of silex ; hence the more rapid attrition of the 

 tooth. 



This may have been the case with the two extinct genera; the different periods during 

 which they lived may have seen a change from forest to prairie. (It is not intended to 

 insinuate that the species of the two genera are necessarily of the same or any given 

 number.) 



[Oct. 



