636 THE AMERICAN NATURALIST.  [Vor. XXXIV. 
table, in which the position of the first hamal arch is un- 
known, but which has three sacral ribs. 
TABLE I! 
* og 
VERTEBRA WHICH > g First HÆMAL ARCH ON 
CARRIES SA- E z me 
z P Vertebra 22. Vertebra 23. Vertebra 24. | Vertebra ? 
AEN S Ee 81 30 33 18 
XM ee ee 16 4 2 IO 
RAP oi I I 
R. XVIII ^ ^ 
LI OSLX QS. 
BR AIX uz. 
L. XVIII , i 
RKFXRIX 1.11 
EXT. 5. 3 3 
REGNA. 
Lx. 5 2 I 3 
ER AVHI ... 
Lt xVHLXIx| ' I 
AIR v. i 
Loxp xx : I 
R AIS SA 
Lu R s I 
Tol. iv. 114 | 34 = 41% of 82 | 44 = 54% of 82 | 4— 55 0f 82| 3? 
Some of the data listed in the above tables deserve further 
mention. One of the most striking points is the occurrence of 
as many as five individuals having three sacral ribs. Waite 
mentions one such instance, which I think is the only one 
previously recorded for JV. maculosus, while among the 114 
individuals examined by us there are four such cases. One of 
these has, as an additional peculiarity, two sacral ribs on the 
eighteenth vertebra, and is the first one recorded in which that 
vertebra is invaded on both sides. The figure shown on P. 638 
represents the eighteenth, nineteenth, and twentieth vertebra 
1 R. and L. are used as abbreviations for right and left. 
