274 DR. A. RATTRAY ON THE ANATOMY, PHYSIOLOGY, 
Classification. | 
The literature of the Heteropoda, especially its lower forms, is trammelled with that 
unfortunate tendency to excessive multiplication of names, and indefiniteness in classifi- 
cation, so common in many departments of natural history—as if zoologists, in meeting 
with, to them, new or like varieties, were undecided in what family or class to place 
their specimens, and, unimpressed with the importance of correct and systematie tabu- 
lation, got out of the difficulty by sketching and giving a new synonym fto an animal 
perhaps already known and in the enjoyment of several titles. Hence greater accuracy 
in defining species and varieties, a lucid and not too minute arrangement, and a simple 
easily understood nomenclature, at all times a desideratum in scientific research, are well 
worth attempting with the Heteropods, and fortunately is comparatively easy, as a careful 
survey of all that are known will show that they may be severally ranged in different 
groups, each possessing distinctive characters. 
Even on limited observation, nothing can be more evident than how readily the diver- 
sities in their structure may be turned to account in determining varieties when external 
configuration alone makes discrimination difficult. Such minute and careful microscopic 
examination as that of the lingual dentition is too troublesome to be generally available; 
and we naturally seek for some easier means by which we may at once, and, if not by 
the naked eye, at least by a low magnifying-power, fix the position of specimens as we 
meet with them. This may be readily accomplished by attending, first, to the presence or 
absence of a shell; second, to the character of the visceral nucleus, whether pedunculated 
or forming part of the soma; third, its position with regard to the tail proper; and, 
fourth, the presence or absence of a breathing-apparatus and its nature. A very Cursory 
glance at the order will show that its different varieties may be conveniently separated 
into two primary divisions. 
lst. The Atlantidæ, including Atlanta and Oxygyrus, whose bodies are curved and 
capable of being wholly retracted into a spiral shell; and, 
2nd. The Firolidæ, including the Carinaria, Carinaroides, Firola, and Firoloides, 
whose form is straight and elongated, and either wholly naked or furnished with a very 
small shell, covering the appendicular visceral nucleus. 
The difference between these is so marked that it is easy to refer specimens to either. 
But it is with the members of the second that the chief difficulty appears to lie; and we 
, find them variously divided and profusely named by terms often apparently indis- 
criminately used—so much so that there is some trouble in ascertaining what is or which 
is an Anops, a Pterotrachea, Firola, Firoloides, Carinaria, Cardiapoda, Cerophera, or 
Carinaroides, and in wading our way to safe conclusions amidst a confused multitude of 
soubriquets and the application of double and even triple names to the same variety. 
The presence or absence of the rudimentary shell and the character of the branchial 
nucleus, however, enable us to further safely and easily subdivide the Firolidze into :— 
_ Ast. The Carinaria, with a vitreous shell, and the Carinaroides or Cardiapoda, with a 
cartilaginous or horny one, protecting the visceral nucleus, which is pedunculated ; and, 
2nd. Firola and Firoloides, which are destitute of a shell, and have a sessile visceral 
nucleus. 
