1889.1 [Allen. 



of that species. The metacarpal of the first digit is of the same length in 

 one specimen of C. brevicanda, while the first phalanx is shorter than in 

 any. The head is shorter while the ear is longer. The tragus remains 

 the same in the two species. The thigh and the leg are both shorter in 

 G. castanea, while the tail is absolutely longer by 1 mm. 



The proportion ot the widths of the second, third and fourth interdigital 

 spaces is shown to he subject to variation. Specimens numbered 3129, 

 3231, 3128, 3230, 3229, and 4192 are of those in the best condition ; and it 

 is seen that the differences are less than in the remaining specimens. 

 But after all possible sources of error are eliminated, it will be seen that in 

 three only of G. brevicauda (the males, Nos. 3230, 3229, 4192— and thus 

 suggestive of sexual distinction) is the difference between the widths ot 

 the second and third spaces less than 10 mm., while in the single example 

 of G. castanea (also a male), the difference amounts to but 9 mm. 



In this connection I may allude to the value which attaches to the last- 

 named measurements in the study of the Cheiroptera. 



If a specimen of a bat, which is preserved in spirit, is so held in the hand 

 that the wing is supported in the position of flight, it will be seen that the 

 intervals between the metacarpal bones hold a definite relation to each 

 other. 



The width of the spaces between the metacarpals, now being recorded 

 (the measurements are taken at their widest parts), it will be seen that 

 the second interspace is the narrowest and the fourth the widest. In this 

 way a formula may be stated. It is proper to add the length of the fore- 

 arm to the formula, since this measurement is one of relative constancy 

 and is of importance in framing the diagnosis of the species. 



Examination of the table herewith presented exhibits at a glance the 

 marked contrasts which obtain in the Phyllostornidoe in the composition 

 of this formula. 



It is especially interesting to note the difference which exists between 

 the widths of the second and the third interspaces. It will be observed that 

 no two formulae are alike, nor is any fixed ratio preserved between the 

 formulae of genera which are allied. Nevertheless the measurements are 

 sufficiently distinctive to warrant the recommendation that they be taken 

 in all discriminating studies, not only of the Phyllostomidse, but of the 

 entire order. 



Formula of the Widths of Second, Third and Fourth Interspaces in the 

 Genera of Phyllostomidw. 



ii in iv Forearm. Differ'ebet. iii&iv 



mm. mm. mm. mm. mm. 



Lophostoma 7 17 18 49 1 



Schizostoma 3 16 21 32 5 



Macrotus 2 15 22 44 7 



Desmodus 2 21 37 53 10 



Vampyrops 3 17 27 36 10 



PROC. AMER. PHILOS. SOC. XXVIII. 132. D. PRINTED FEB. 25, 1890. 



