150 CONCHODERMA VIRGATA. 



states that many individuals are light-brown or yellowish- 

 grey, with irregular brown streaks, or crowded dots : 

 he states that in very young specimens the colours are 

 paler, and the valves spicular. 



Size. — The largest specimen which I have seen, had a 

 capitulum rather above one inch long and three fourths 

 of an inch wide : growth very rapid. 



Monstrous Variety. — In the British Museum, there is 

 a dried and somewhat injured specimen of a monstrous 

 variety, the Pamina trilineata of J. E. Gray : it differs 

 from the common form only in having a tubular projec- 

 tion, just behind the notch separating the upper points of 

 the terga ; this tube springs from over the terga, and is, 

 therefore, in a different position from the ear-like append- 

 ages in ConcJioderma aurita. It does not open into the 

 sack : the membrane composing it appears to have been 

 double in the upper part, and to have been lined with 

 corium : in short, this tube seems to have been an ex- 

 crescence or tumour, of a cup or tubular form. 



General Remarks. — It will have been seen how much 

 subject to variation the valves of this species are. When 

 I first examined the Cineras cJielonophilus of Leach, from 

 36° N. lat., Atlantic Ocean, and found in many specimens, 

 both old and young, that the terga were very small, flat, 

 acuminated at both ends, with a projecting shoulder on 

 the carinal margin, and situated at about their own 

 length from the apex of the carina, and at twice their own 

 length from the scuta; and when I found the carina 

 acuminated at both ends, and the scuta very imperfectly 

 calcified, with the lateral lobe broad, flat, and standing 

 out at right angles ; and lastly, when I found the whole 

 capitulum bluntly pointed, instead of being square on 

 the summit, I had not the least doubt, that it was a 

 quite distinct species. Afterwards, I found in the Cineras 

 Olfersii of Leach, from the South Atlantic, the same form 

 of terga ; but within slightly more concave or furrowed, 

 and not nearly so small, and therefore not placed at above 

 half so great a distance from the other valves ; and here, 



