188 J. E. DurrpEn—Jamaican Actiniaria : 
dichrotecus, Hadd. and Shackl., but histological characters reveal that the two are 
quite distinct. I propose to term it Parazoanthus tunicans, on account of its 
investing habit. 
Quantities of sponges were also trawled on the same occasion, many of which 
displayed small commensal anemones distributed over nearly their whole surface. 
On some massive, black sponges, two or three feet in diameter, the polyps 
appeared as distinct, white, circular discs, but on a dark, purplish sponge they 
were in small colonies, producing short catenulations. 
A detailed study discloses that these two, though somewhat similar in their 
habit, are distinct species. 
Anatomical examination leaves no doubt that the first sponge-incrusting form 
is a Parazoanthus, and I propose to term it.P. separatus, in emphasis of the distinct 
character of its individual polyps. With regard to the generic position of the 
second, some uncertainty prevails. Owing to the remarkable shortness (0°5 mm.) 
of the polyps, and the presence of numerous large sponge spicules in the capitular 
region, I have failed to make out the arrangement of the mesenteries, or to 
discover any sphincter muscle. 
Considering, however, the extreme weakness of the musculature in all the other 
parts of the polyp, and the thinness of the mesogloea in the capitulum, there can 
be no doubt that any sphincter occurring will conform to the type characteristic 
of Parazoanthus; and further, comparing all its external and anatomical features 
with those already known in other species, I have little or no hesitation in 
assigning the form to the present genus. I propose for it the term Parazoanthus 
monostichus, the polyps being usually arranged in a single row. 
A comparative study of the different representatives of the genus calls for a 
few remarks of more general interest in Actinian morphology. 
In respect to both its musculature and the mesenterial filaments, Parazoanthus 
displays conditions which lead one to place it as the lowest of the Zoanthean 
genera, a position already assigned it by Haddon and Shackleton on less 
conclusive grounds. ‘Taking the mesenteries only into account Haddon considers 
the other sub-family—the Brachyenemine—may be regarded as slightly more 
primitive. 
The musculature in all the species of Parazoanthus is weak. This is especially 
true of the sphincter muscle. In all other genera of the Zoanthide the sphincter 
is embedded in the mesogloea, and is usually of considerable strength; in 
Zoanthus it is even double, being subdivided into an upper and a lower portion. 
The diffuse, endodermal sphincter characteristic of the genus represents 
merely a concentration in the capitular region of the circular endodermal muscle 
which lines the column, usually throughout its length. 
As the sphincter becomes more strongly developed, the mesoglceal foldings 
