VAN NAME: SIMPLE ASCIDIANS. 605 
lata are in the collections, they are for the most part so poorly pre- 
served that anatomical differences might easily escape notice, and the 
writer is familiar only with the southern form (ocellata) in a fresh 
state, never having himself collected the northern form {tenella). 
Professor Verrill assures the writer that when fresh there is a notice- 
able difference between the two, tenella though occasionally as large 
as the other form, averaging of smaller size (usually not over 30 mm. 
or 40 mm. long) and being of softer and more flaccid consistency than 
ocellata, which often becomes 60 mm. or more long and has a firmer, 
more rigid test. Even in alcoholic specimens these differences are 
often noticeable, though the circumstances of collection and preserva- 
tion may greatly alter the character of the test. The writer would not 
attribute the weight of specific characters to these differences, yet 
under the circumstances he does not feel justified in ignoring them 
entirely, and in giving the synonymy and the distribution of this genus 
in the New England region will distinguish between the northern and 
the southern forms by using the names tenella and ocellata for varie- 
ties. The relations of these forms to those of the other parts of the 
world cannot be determined without the comparison of more material 
than has yet been available, and the writer must leave that part of 
the question unsettled. 
In both forms the body is elongated oblong and generally somewhat 
tapering toward the anterior end, and compressed laterally, adhering 
by the larger (posterior) end; the orifices on short tubes, near to- 
gether, the branchial the larger and terminal, the atrial smaller and 
more to one side. Most specimens are, however, more or less dis- 
torted and unsymmetrical, and in preserved specimens this is further 
increased by the unequal contraction of the muscles. The test is of 
varying thickness, more or less transparent, showing clearly the mantle 
(which is pale yellowish during life) with its muscle bands, as well as 
the alimentary and reproductive organs. The branchial orifice has 
eight, and the anal orifice six red or orange spots (ocelli) about its 
margin, but these fade out in preserved specimens. 
The musculature of the mantle is one of the most conspicuous char- 
acters. There are a number of broad strong longitudinal bands on 
each side extending nearly the whole length of the body. Outside 
these are fairly numerous but very narrow circular muscles, not 
gathered into definite bands. The sphincters of the siphons are well 
developed. 
