MALACOZOA. TROPIOPODA. LAMELLIBRANCHIATA. 293 



angulate form and bordering the elongated marginal groove ; 

 in the left valve a corresponding concave tooth, and a similar 

 umbonal toothlet, with an anterior sinus, the margins plain. 

 When free of epidermis, it is glossy white ; that membrane, 

 which is very delicate, being yellowish-grey, and when present 

 giving that tint to the shell. 



The shell is not very unlike Tellina tenuis of the same size, 

 but much more convex, and with the external ligament not a 

 fourth of the size of the ligament of that species. 



Found by my daughter, Anne, while with me, on the sands 

 at Don-mouth, cast ashore in considerable numbers, along 

 with Tellinse tenuis and Fabula, after a heavy ground-swell, 

 which destroyed the greater part of the stake-nets from the 

 Dee to the Ythan, in September, 1842. Two days after 

 gathered there by me, along with Dr. Fleming and Mr. Leslie. 

 Afterwards found alive by my daughters, Isabella, and Anne, 

 and my son, Paul Howard, in the mud of the estuary of the Dee. 



The animal is of a yellowish-white colour, with the foot very 

 large, compressed, broad, bent, obtuse at the lower margin and 

 tip, minutely scrobiculate, and subcartilaginous, the siphon- 

 tube short, the upper siphon very small, cylindrical, and at 

 the end free from the lower, which is three times the size and 

 somewhat compressed ; the branchiae very unequal ; the mantle 

 open unless behind, with the margin crenato-denticulate. 



Mactra Boysii. Mont. Test. Brit. 98, PI. 3. f. 7. Amphidesma 

 Boysii. Turt. Brit. Biv. 53. PI. 5. f. 4, 5. Amphidesma album. 

 Flem. Brit. Anim. 433. Mactra alba. Wood, Linn. Trans, vi. 174. 

 PI. 16. f. 9-12. Amphidesma Boysii. Lamk. Syst. v.491 ; Ed. n. 

 vi. 128. 



2. Amphidesma tenue. Triangular Amphidesma. 



Shell ovato-triangular, nearly isomeral, obsoletely striated 

 concentrically ; the valves thin, semitransparent, hyaline-white ; 

 the umbones prominent, small, direct; in one valve, a cleft 

 toothlet, and two lateral laminar teeth, besides the oblique 

 concave space ; in the other valve a simple toothlet and two 

 marginal grooves ; the inner surface glossy, with faint radiat- 

 ing striulae, and a deep sinus in the pallial impression. Length 

 half an inch, height four-twelfths and three-fourths. 



Several single valves found in shell sand, from Cruden Bay, 

 sent by Mr. Murray, in November, 1842. 



Mactra tenuis. Mont. Test. Brit. 572. PI. 17. f. 7. Amphi- 

 desma tenue. Turt. Brit. Biv. 53. Amphidesma tenue. Flem. 

 Brit. Anim. 433. 



