PLATE LVI. 
gists at this time, to be specifically different. Linnaeus describes 
them in the same words, observing only, that the body in Typhle is 
Sl X sided, while that of Acus has seven sides. The seventh angle 
in Acus, is formed by the raised line that extends longitudinally 
along the belly, commencing at the throat, and reaching down to 
the vent. This line in Acus is prominent and distinct. In Typhle 
Such a line is observable likewise, traversing the center of the abdo- 
minal plates in a similar manner, but it does not assume the strongly 
e levated form of a carina as in Acus. 
Linn reus regards the number of annulations in those species, only 
as secondary to his specific characters. In this respect, he is per- 
fectly right. We have examined many of both kinds, and find that 
although in point of number there is generally an agreement between 
ffe specimens of each individual sort, they are not constantly 
file same. For instance in Typhle, the number of whose joints are 
stated at 18 in the trunk, and 36 in the tail, we have found instead 
’with 18... 37 — 19... 36 — and 17.. .42, the latter nearly corresponding 
'with Acus. And Acus which is said to have 20 joints in the trunk, 
a ud 43 in the tail, is also susceptible of variation. 
This irregularity in the number of the annular joints, leads us to 
have recourse to other characters, in which respect the structure of 
file snout appears more constant than almost any other. So far as 
We have been able to ascertain the circumstance, this may be trusted, 
hi all the specimens of Typhle we have examined, the snout is large, 
htoad, and sub-compressed on the sides. It passes from the crown of 
file head, which is fiat, to the mouth, in a straight line, or with veiy 
little sinuosity ; instead of which, in Acus, the outline from the nape 
0v er the crown of the head rises conspicuously, then takes a curva* 
