|. Chiton known to 
396 
and broken into incipient, flattened pustules. Insertion plates, 
porcelain white, slits five, broad. . 
Posterior valve.—Mucro very distinct, posterior, the 
anterior portion of valve is similar in sculpture to the pleural 
. and lateral areas in other valves. A diagonal depression 
separates this from the posterior portion, the ribbing being 
deflected downwards and its character somewhat altered, the 
ribs here showing a tendency to become granulose, still further 
changing when the posterior part of valve is reached, the shell 
there being covered with closely-packed granules without any 
system of arrangement. Insertion plates white, one broad slit 
on each side and four, and suggestion of a fifth, immediately 
ing in places; this feature may more marked in other 
specimens. bog 
The pleural area is covered with close, wavy, longitudinal 
ribbing, the ribs are more abrupt on the lower side, and the 
? . 
laminae produced very little forward, sinus broad and sinuate. 
Measurements.—35 mm x 11 mm. in dried specimen. 
ulf St. Vincent, South Australia. Up to the present only 
one specimen has been met with. The type will remain for the 
present in Dr. Torr’s collection, but ultimately it will be placed 
in the South ‘Australian Museum. 
Remarks.—This species can easily be distinguished fous 
Notoplax matthewsi, Bed. and Pils., by the ribbing being 
continuous and not broken into granules, the ridges are less 
strong, and the pinnatifid- character of the dorsal area, 1 
marked in V. matthewsi, is almost absent in this species. 
is more nearly allied to that species than to any other Acantho- 
me. The specific name is derived from the 
Latin porca, meaning a ridge between furrows. 
