SIPUNCULOIDEA. 137 
two varieties which in the account of Dr Willey’s Sipunculoids I distinguished as S. vastus 
albus and S. vastus obscwrus were very marked and Mr Gardiner notes that some of the 
former were translucent whilst others were opaque, a condition possibly depending on the 
state of the contraction of the muscles. He notes that they take no part “in the dis- 
integration of the rock. It was most noticeable that while the coral masses were bored 
into by various forms of Sipunculoids, the sand rock everywhere was absolutely free from 
all living organisms.” 
II. ON THE NEW GENUS LITHACROSIPHON (Plate VII). 
LITHACROSIPHON nov, gen. 
Lithacrosiphon maldivense nov. sp. 
A very peculiar form of Sipunculoid was represented in this collection by a single 
specimen. It was 3cm. long and averaged about 4mm. in breadth. The great peculiarity 
of the animal is that the anterior end of the body is armed with a solid conical cap of hard, 
calcareous (?) matter. This cap has the shape of the ‘sugar-loaf’ astrakan hats sometimes 
worn in Turkestan. The ventral outline of the cap, which runs from the apex to the point 
where the introvert opens, is straight and in a line with the general surface of the body, but 
dorsally the surface of the cap slopes down at a sharp angle with the ventral surface to 
just above the position of the anus. The straight ventral edge of the cap is 3 mm. long, 
the sloping dorsal edge 5 mm., the width of the cap at its widest, ie. just where it is 
inserted into the body, is 83mm. The cap is borne by a pad of skin, which forms the 
anterior end of the body, and into which the longitudinal muscles of the body-wall are 
inserted; this pad is almost transverse to the long axis of the body, but slopes a little 
from the anteriorly placed orifice of the introvert to the slightly more posteriorly placed 
anus. The hinder half of the stony cap is of the same deep chestnut colour as the body, 
and it has the appearance of being covered by a thin extension of the skin, but the 
anterior pointed half is naked, white and almost glistening. 
The cap exhibits a certain laminated structure probably due to lines of growth. If 
found fossil, it could easily be taken for the end of a belemnite. 
The general colour of the animal varies in the specimen, which had been preserved 
in spirit, from a deep chestnut-brown at the two extremities of the body to a greyish 
yellow in the middle where the skin becomes sufficiently transparent to show the bundles 
of longitudinal muscles. Anteriorly the skin, surrounding the base of the cap, is raised up 
into very numerous tubercles, some of which are arranged somewhat symmetrically round 
the orifice of the introvert and around the anus. The latter opening is a transverse slit 
and slightly elevated. The skin is thick and tuberculated for about the anterior sixth 
of the body, but it gradually thins and loses its tubercles and becomes transparent. In 
my specimen this is the stoutest part of the body, but outline counts for little in a 
Sipunculoid. Posteriorly the skin again becomes dark and opaque and covered by brown 
patches; the skin however hardly thickens, and there is no sign of any posterior shield, 
such as is so characteristic of the genus Aspidosiphon. 
The internal anatomy is simple. The introvert in the specimen is fully retracted, and 
measures from the anterior end to the position of the head about 1 cm. in length. The two 
18—2 
