NO. 4 HOPLOMYS (THICK-SPINED RATS) HANDLEY 5 



which it was compared. The degree of reduction of dorsal doming and 

 ventral depression of the brain case of the Escudo specimen is reflected 

 in the convergence of greatest and condylobasal lengths of the skull, 

 and in the more posteriorly oriented (as opposed to ventrally 

 oriented) foramen magnum. 



The thick spines that distinguish Hoplomys are longest and 

 strongest just behind the shoulders on the upper midback, from 

 which point they diminish in size in all directions. The spines possibly 

 vary geographically in size. They appear to be longer and stronger 

 toward the southern part of the range of Hoplomys. The Escudo 

 specimen, although it is larger than any other, has the smallest and 

 weakest spines. Maximum spine length varies as follows (mean, 

 followed by extremes) : 6 Ecuador 29 mm. (28-31), 4 Darien 30 

 ( 2 &-33)> XI Cerro Azul 28 (26-29), 5 Canal Zone 28 (27-30), 

 1 Escudo de Veraguas 26. 



Coloration of the spines is individually variable. All specimens 

 have all spines proximally white and distally colored. The tips of those 

 of the dorsum are always black, but the flank spines usually are tinged 

 with orange or banded with orange and black distally. Occasionally 

 the flank spines are colored like the dorsal spines. 



Coloration of the soft hairs of the dorsum is geographically variable. 

 At the southern extreme they are reddish orange, especially on the 

 shoulders. The soft hairs of the Escudo specimen are similar but 

 darker and brighter. Costa Rican and Nicaraguan examples have the 

 hairs more orange, and those from Panama and northern Colombia 

 are more yellowish on the average. The presence or absence of black 

 ocular and crown areas appears to be individually variable throughout 

 the range of Hoplomys, but only the Escudo specimen has the soft 

 hairs blackened to form a distinct middorsal stripe from snout to base 

 of tail. 



All populations have the underparts dominantly white, and all have 

 some individuals that show encroachment of agouti hairs of the side 

 neck onto the throat, suggesting an incipient collar. This is well 

 marked in the Escudo specimen; one from Rio Indio, Canal Zone, 

 has a complete collar. Nine of the 14 Cerro Azul specimens have 

 clear orange collars, and several of them have a band of clear orange 

 hairs separating the agouti hairs of the flanks from the white hair of 

 the belly. Neither of these features is seen in samples of other popu- 

 lations. Coloration of the forefeet (usually white on the inner side, 

 colored on the outer, occasionally colored throughout), and coloration 

 of the cheeks (clear orange, buff, gray, or agouti) are individually 

 variable. 



