1 76 
cimens of this shell I was favoured with by the Rev. Mr. Cleeve, and 
by Mr. Clarke. 
T. aliformis. A wing-shaped ribbed shell. The first ribs, which 
commence at the beaks of the shell, are transverse, but acquire a slant- 
ing direction as they fill up the posterior part of the disk, until those 
which terminate in the superior margin, become longitudinal, and are 
thus continued to the anterior termination of the shell. The ribs of the 
posterior side augment in size as they proceed to the margin ; but those 
which are disposed on the anterior side, are of the same size through 
their whole length. On the inferior, or rather anterior side, is a wide 
excavated area, on each side of the cartilaginal depression and the mar- 
gin of the shell, on which transverse ribs are disposed. Plate XII. Fig. 9. 
This specimen, which was in Dr. Menish’s collection, I was presented 
with by Captain Gardiner. 
T. dcedalea. Of this shell I only possess the fragment Plate XII. 
Fig. 6, from which it is impossible to speak of the form of the shell 
The anterior side and cartilaginal area appear to have been very wide. 
The disk is ornamented with granular and nodular projections, disposed 
in daedalean windings, so pecular in their dispositions, as to allow the 
assuming of this as a specific distinction. 
T. spinosa. A suborbicular shell, the whole of the disk covered with 
ribs formed of spinous tubercles. The ribs curved, commencing at the 
beaks in a transverse direction, passing over the middle of the disk in an 
oblique, and at the superior margin, approaching to a longitudinal di- 
rection. The area on the anterior side of the shell is also covered with 
curved transverse ribs, formed of small tubercles. Plate XII. Fig. 
This specimen I was favoured with by Captain Gardiner, from Dr. Me- 
nish’s collection. 
It is true, that in this specimen the appearance of the projections is 
more that of tubercles than of spines ; but, on inspection with a lens, I 
find that most of these are broken ; and, on examining another speci- 
men, a part of a valve of indubitably the same species, I discover that at 
