358 Mr. A. II. Clark — An interesting 



It is evident from Ryder's definition of " gephyrocercy " 

 that this term will have to be restricted to the Molidae, where 

 the posterior part of the tail seems to have aborted and the 

 interval between the dorsal and anal has become bridged 

 across (yecpvpa, bridge) by a secondary formation of rays, 

 inserted on basalia and derived from the dorsal and anal fins. 

 In a number of eel-shaped fishes the dorsal and anal fins are 

 confluent with the caudal, which becomes progressively 

 reduced as the tail gets longer and the vertebras and dorsal 

 ?nd anal fin-rays increase in number. The Ophidioids are 

 fishes of this type ; in Genypterus the last vertebra is slightly 

 expanded posteriorly into two hypurals, one of which bears 

 four and the other five rays, the remnant of the caudal fin. 

 Emery's figure of Fierasfer dentatus shows a condition some- 

 what more specialized than in Genypterus ; there is no definite 

 hypural expansion and the last vertebra is almost like the one 

 in front of it, but without neural spine; the caudal rays, 

 distinguished by the absence of basalia, are now only six in 

 number. F. acus appears to differ in that the caudal fin has 

 disappeared, whilst the end of the tail projects beyond the 

 dorsal and anal, as in the Ophichthyid eels. 



XLIX. — An interesting Structural Analogy. 

 By Austin Hobart Clark. 



Every ornithologist is aware of the fact that in the winter 

 the Ruffed Grouse (Bonasa umbellata) and related species are 

 enabled to tread upon the loose surface of newly fallen snow 

 without sinking down into it, through the seasonal develop- 

 ment of the so-called " snow-shoes," which greatly increase 

 the area covered by the soles of the feet. These " snow- 

 shoes " are composed of two rows of scutes on either side of 

 each toe — the first row, adjoining the median scales, similar 

 to them and more or less squarish ; the second row smaller, 

 elongate-oblong, and projecting laterally outward when the 

 foot is on the ground, downward and slightly forward when 

 the foot is raised. The area covered by each foot of the 

 Ruffed Grouse in the winter, therefore, is equivalent to the 

 area covered in the summer plus the area covered by these 

 lateral scutes, or about as much again. Thus a bird walking 

 about in the winter brings to bear only half as much weight 

 in any given spot as the same bird in the summer, and is 



