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united to the body, so that the dorsal channels are only closed by 
the apposition of the parts. 
The outer gills are simpler in structure, being formed of a single 
series of vascular loops placed one behind another ; the free edge is 
not grooved, and the gill terminates in front some way behind the 
inner gill. The dorsal margin of the outer lamina is expanded be- 
yond the line of suspension, and is fixed. 
The gills of the opposite sides are united to each other behind the 
body and to the branchial septum. 
The whole structure is closely like that of Mya arenaria, the 
chief differences being the shortness of the palpi, and the inequality 
of the gills. 
There are six other reputed species of recent Panopea. 
1. P. appreviata, Val.; discovered by M. d’Orbigny on the 
coast of Patagonia between the R. Negro and 8S. Blas. ‘This shell 
appears to have been again met with by the U. 8. Exploring Expe- 
dition, under Commander Wilkes, and is described by Dr. Gould as 
P. antarctica. 
2. P. zeLanpica, Quoy ; of which an odd valve only was picked 
up on the beach. 
3. P. soranpri, Gray; probably the same as the last. 
4. P. ausrrauis, G. Sby. (Genera of Shells, pl. 40. f. 2), one of 
G. Humphrey’s shells from New South Wales; of which there is a 
series in the British Museum, from Tasmania. 
5. P. ausrrauis, Val. (not Sowerby’s.) 
This species is as large as P. Aldrovandi, and very like it. Bemg 
quite distinct from the P. australis of Sowerby, it is proposed to call 
it P. natalensis. 
It was discovered in the sandy bays of Port Natal, by Capt. Cecile 
and the officers of the French frigate ‘ Heroine,’ who observed the 
tubes of the shell-fish projecting through the sand at low water. 
‘The sailors endeavoured to draw the creature out of its habita- 
tion by the tube, but in vain; for the siphons, after offering con- 
siderable resistance, in every instance gave way, and often were with- 
drawn entire, in spite of the grasp of its persecutor. Curious to 
know the nature of the being which thus escaped them, they dug for 
it with spades, and at length uncovered the Panopea buried several 
feet below the surface of the sand, and gregarious*.”’ 
6. Panopama saponica, A. Adams. Zool. Proc. for 1849, p. 170. 
Pl. VI. f. 5. This species, of which the original and unique exam- 
ple is in the Leyden Museum, is much like the fossil P. intermedia 
of the London clay. 
7. P. cenrerRosa, Gould; Puget Sound, Oregon. (U.S. Expl. 
Exped.) 
3. Panop#a norveeica, Spengler, is found throughout the 
Arctic seas, from Behring’s Straits to Newfoundland, the North Sea 
and Russian Lapland. 
I was so convinced of the affinity of this shell to the Sawcava, that 
(in my Manual) I placed the latter genus next to Panopea ; it now 
* Forbes, i. p. 174, from Valenciennes’ Archives du Museum, t. i. 1839. 
