176 



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 com- 

 mence at the beaks of the shell, are transverse, but acquire a slanting 

 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 pos- 

 terior 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. d&dalea. 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 appeal- to have been very wide. 

 The disk is ornamented with granular and nodular projections, disposed 

 in daedalean windings, so peculiar in their dispositions, as to willow 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 direc- 

 tion. The area on the anterior side of the shell is also covered with 

 curved transverse ribs, formed of small tubercles. Plate XII. Fig. 7. 

 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 



