( 108 ) 
This result leads us to a dilemma. Either the definitions of sigma- 
spira and toxaspira will have to be modified, or we have to drop the 
distinction between the two forms of spicula. I believe that it follows 
from the above table that the latter way out of the difficulty is 
preferable. We may maintain the name sigmaspira for smooth, 1. e. 
not spined a-spiraxons of no more than 1°/, revolution. 
LENDENFELD (1890 p. 425) has another conception of the sigmaspira : 
“ein einfach spiralig gewundener oder bogenförmiger Stab.” Hence 
he seems to accept two different kinds, instead of considering them 
as belonging to one sort, the shape of which simply differs according 
to the direction in which it is viewed. Since he says that his “spiral” 
has “mehr wie eine Windung”, he seems to accept no more than 
one revolution for the sigmaspire. This is not in accordance with my 
observations, as laid down in the above table. 
2. Spirula. 
Although Carrer did not give a special definition of the spirula, 
it is clear enough what he understands by this name. In his paper 
on the “spinispirula” (1879 @ p. 356) he calls the spiculum which 
he formerly (1875 p. 382) described as “sinuous subspiral’, simply 
“the smooth form of the spirula” and he refers to an illustration of 
the spicule as it occurs in Cliona abyssorum (1874, PL XIV, p. 33). 
Obviously the term spirula used by Carrer is an abbreviation of 
4spinispirula’, not as terminus technicus. Riprey & Drnpy (1887 pp. 
XXI and 264) introduce the term spirulae as synonym with spinispirulae 
of CARTER, adding that “these are more or less elongated, spiral or 
subspiral forms, which may be either smooth or provided with more 
or less numerous spines.” SoLLAS creates (1888 p. LXAII) the term 
polyspire for spirula, stating that it is 4a spire of two or more revo- 
lutions”, adding, however, that he is inclined to adopt the term spirula. 
In the list given by ScnutzE & LENDENFELD (1889 p. 28) we find a 
Ispirul” described as “spiral gewundene Nadel mit mehr als einer 
Windune”. Consequently we learn that the term spirula by some 
authors is used both for smooth and for spined forms, whereas others 
leave the question open. LENDENFELD (1890 p. 426) proposes the 
name for smooth spicula only: “eine sehlanke und glatte, spiralig 
gewundene Nadel mit mehr wie einer Windung”. I herein agree with 
LENDENFELD and I understand by spirula: a smooth e-spiraxon of at 
least 1°/, revolution. 
3. Spinispira. 
As long as the a-spiraxons are smooth it will as a rule not create 
any difficulty to distinguish sigmaspirae and spirulae. But there are 
