FLORIDA MUSKRAT. 327 



to those of Fiber. Between the maxillary and squamosal processes ex- 

 ternally the malar is reduced to a mere thread, as in that penus.* 



The strai)-sha[)ed process of the squamosal bounding" the squamosal 

 fenestra stands nearly, vertically, and the constrictioji of the skull be- 

 tween the fenestr?e is less than in Fiber. The anterior margin of the 

 mcaiuH auditorius is much less prolonged than in that genus. The bullae 

 are more intlateil. The surface of the mastoid is uneven, but not strongly 

 concave; the foramen ver^- small. 



The coronoid process of the mandible is not as high as the condyle, 

 but the jaw is not otherwise different from that of Fiber. 



The anterior upper molar has five cusps, the first not wider than the 

 other, nor compressed. The second molar has four cusps, the anterior 

 largest, acute externally, rounded internally. The posterior molar has 

 four cusi>s, the anterior like that of the preceding tooth, the second and 

 tliird equal in size, the last half-halberdshaped, and almost or quite 

 external to the median line of the series. The anterior lower molar has 

 seven cusps, the first irregularly halberd-shaped, the last almond- 

 shaped, the rounded end internal. The second tooth has five cusps. 

 The last has four cusps, of which the first three are very small and the 

 last rhomboidal. 



The skeleton presents a numl)er of peculiarities, aside from propor- 

 ^tions, which distinguish it from that of i^. zibethiciis. The inferior lam- 

 ella of the transverse process of the sixth cervical vertebra is short and 

 broad, and does not extend bac^ under the head of the first rib, as in 

 F. zihcthicns. The neural spines of the dorsal vertebrae are much higher 

 than those of the lumbar vertebrae, the reverse being true in the case of 

 Fiber. Of the six segments of the sternum the fifth is the smallest, being 

 one-half as high as broad. Tlie transverse processes of the lumbar 

 vertebrae a:e short, and do not extend to the level of the under side of 

 the centra. The processes of the caudal vertebrae, after the fourth, are 

 ludimentary ; the vertebrae themselves are much elongated. 



The anterior extremity presents no special distinguishing character- 

 istics. In the pelvis the acetabulum is situated at the junction of the 

 third and fourth fifths of its length. There is less difference in the os- 

 seous structure of the ieet of the two muskrats than one would sui)i)Ose 

 from an examination of the exterior. The peculiar bending of the toes 

 in Fiber appears to be due to muscular and ligamentary antagonism 

 rather than to any peculiarities in the arrangement of the bones of the 

 foot. In Ncofiber the fifth metatarsal is not more than one-half as long 



as the second, and the first is but little longer. In Fiber the second 



. — * 



"Mr. N. P. Scndder (Proc. Biol. Soc. Washington, ii, ld85, p. Ixivj very justly takes 

 exception to Dr. Coues's statement that in Fiber tbe squamosal ami maxillary spurs 

 are in contact on the outer side of the zygomatic arch (Monogr. N. A. Rodentia, 1677, p. 

 253). Such an arrangement of" parts appears to exist only in cxctptional cases, if at 

 all. Among eleven skulls in the Museum collection there are none in which the two 

 spurs are absolutely in contact, though in one the space between them is exceedingly 

 narrow. 



