220 



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 Panopcea. 



1. P. abbreviata, Val.; discovered by M. d'Orbigny on the 

 coast of Patagonia between the R. Negro and S. Bias. This shell 

 appears to have been again met with by the U. S. Exploring Expe- 

 dition, under Commander Wilkes, and is described by Dr. Gould as 

 P. antarctica. 



2. P. zelandica, Quoy ; of which an odd valve only was picked 

 up on the beach. 



3. P. solandri, Gray; probably the same as the last. 



4. P. australis, G. Sby. (Genera of Shells, pi. 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. australis, Val. (not Sowerby's.) 



This species is as large as P. Aldrovandi, and very like it. Being 

 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 Panopcea buried several 

 feet below the surface of the sand, and gregarious*." 



6. Panopcea japonica, A. Adams. Zool. Proc. for 1849, p. 1/0. 

 PI. 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. generosa, Gould ; Puget Sound, Oregon. (U. S. Expl. 

 Exped.) 



8. Panopcea norvegica, 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 Saxicava, that 

 (in my Manual) I placed the latter genus next to Panopcea ; it now 



* Forbes, i. p. 1/4, from Valenciennes' Archives du Museum, t. i. 1839. 



