KELLIA. 227 



The byssal sinus is about halfway up the foot on the 

 posterior side ; and from it the animal produces a very 

 delicate thread, and suspends itself freely (with the beaks 

 of its shell downward) by a single almost inconspicuous 

 fibre, which is strengthened by a double attachment at the 

 top. In this posture it appears to rest for some time, with 

 both tubes open, and the foot partly withdrawn into the 

 shell. According to Mr. Clark, the byssus spun by the 

 kind which is found in rocks consists not merely of 

 delicate filaments such as free individuals of the ordi- 

 nary form throw out when placed in a saucer, but of a 

 membranous plate which cannot be detached without 

 some force. He also says that the larger tube in free 

 specimens (having a thinner shell) is marked with flake- 

 white longitudinal lines, which do not appear in the 

 rock specimens. He found in the ovary of one indi- 

 vidual ova in an advanced state, together with fully- 

 formed testaceous fry. M. Recluz has lately announced 

 the same fact with regard to the variety lactea. The 

 ova mentioned by Mr. Clark, and which through his 

 kindness I have had an opportunity of examining, are 

 bean-shaped, and closely resemble a minute form of 

 Cythere. They are very different from the fry, which 

 are perfectly spherical. Dr. Gordon has remarked that 

 K. suborbicularis is occasionally seen as part of the food 

 of the haddock. Sometimes the shell is extremely thin, 

 and so transparent that the gills are distinctly visible 

 through it, causing the surface to appear obliquely 

 striated. The cartilage is always ruptured and divided 

 when the shell is fully opened, one half being left in 

 each valve. The teeth vary somewhat in shape and 

 relative position. 



This species is the Erycina pisum of Scacchi, Bornia 

 inflata of Philippi, and Oronthea Montaguana of Leach., 



