Mr. W. Clark on the rholadidffi. 315 



the ones on the body, are thin and laminar, and have more the 

 appearance of branchial plates than of ordinary palpi. Notwith- 

 standing these peculiarities they have not the disposition of the 

 blood-vessels of the regular branchiae, being quite smooth on the 

 side next the mantle, and on the other closely striated ; in these 

 respects they are like their discordant fellow-palpi, which are 

 smooth on the side next the body, and striated on the other ; the 

 striated surfaces partially lap on each other ; the external man- 

 tellar palpi are very much longer than those on the body. These 

 appendages are usually considered to be of a tentacular nature, to 

 conduct the aliment into the mouth : that may be; but they have 

 also branchial functions, as they are connected with each other 

 by a very visible artery that coalesces w ith that of one of the main 

 branchiae, and I have not a doubt that leading branchial veins 

 form a similar union with those of the regular branchiae. The 

 liver is anterior, of ample volume, granular, and yellowish green. 



Pholas parva, Pennant. 



Animal thick, subcylindrical, less elongated than its congeners ; 

 body milk-white ; mantle pale bluish white, when deprived of the 

 fugacious light-red epidermis, which, at the closure of the valves, 

 forms a line resembling a suture of a red sandy colour : this di- 

 vision of the body causes each side of it to appear banded. The 

 mantle is closed except an aperture for the foot, and being pro- 

 longed into a long retractile sheath covered with a thick red- 

 brown epidermis, which is aspersed with thickset sand -like red 

 eminences, or minute papillae, that become larger and more in- 

 tense at the termini of the orifices, where its margin is irregu- 

 larly encircled with a fine light browm fringe or rather pile ; 

 within the periphery of this fringe are the siphonal apertures, 

 the branchial one being rather the longest, without cirrhi, but 

 sinuated or escalloped, and marked with a dozen brown and white 

 alternate lines running into the tube ; these at half-contraction 

 have the appearance of short blunt cirrhi, occasioned by the 

 doubling of the brown and white points of the scallops, the two 

 nearest the anal tube being the longest in appearance, with a 

 single one exactly opposite the two ; these however are only de- 

 ceptions, and vanish entirely when the tube is fully expanded; 

 the anal cylinder is pale brown and perfectly simple ; both siphons 

 are destitute of cilia, having only the margins of the sheath finely 

 pilose ; none of the other Pholades are without cirrhi on the 

 branchial orifice. The foot, when at rest, is nearly an oval, but 

 in action it becomes pointed behind and rounded in front ; it is 

 truncate at the base, and fixed to the body by a long round cy- 

 lindrical fleshy pedicle of pale bluish white. The branchiae and 



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