30 PKOCKKDINGS OF THE MA LAC'OLOGICAL SOCIETY. 



Collection. This varietj; has been named by Hidalgo T. Lamarchi. 

 A specimen of intermediate size, 18 inches in length, unites these two 

 forms, showing that the differences pointed out in the Thes. Conch, 

 (vol. V, p. 180) are not constant. 



2. T. MCTiCA, Lamk. (Chenu, lllustratmis Conchyliologiques). 

 This is quite distinct from the forms mentioned above. It has no 

 appearance of lamellae or scales, while the fine radiating liriB are very 

 conspicuous. It seems readily separable from all the otlier species. 



3. T. SQUAMOSA, Lamk. (Thes. Conch., vol. v, p. 180, figs. 2, 7, 

 15). This common well-known species can scarcely be confounded 

 with any other. 



4. T. ELONGATA, Lamk. (Conch. Icon., pi. ii, figs. 2a, b; Tlies. 

 Conch., vol. V, pi. 486, figs. 3, 4). I am compelled to unite with 

 this very variable species Reeve's 2\ compressa (Conch. Icon., sp. 5) 

 and T. rudis (Conch. Icon., figs. 4«, b). It seems to me also that 

 T. lanceolata, Sowerby (Thes. Conch., vol. v, p. 181, pi. 489* fig. 18), 

 is onh' a more than usually lanceolate form of the same. T. elonga- 

 tusima, Bianconi,' is the variety compresm, Reeve. Hidalgo has given 

 the name 2\ Reevei to the shell figured in Reeve's Conch. Icon., 

 fig. 2b, which differs from the type in being more sharply acuminated 

 in front. 



I have exhibited an abnormal form shaped like a Trigonia, and 

 another of the variety compressa, a very curious malformation, in 

 which the animal having formed a very perfect little shell made 

 a fresh start from the umbones, leaving the young shell as a decorative 

 appendage. 



5. T. CKOCEA, Lamk. (Reeve, Conch. Icon., pi. viii, figs. 9ff, b). 

 This is of a very differeiat type from the preceding, but so variable in 

 form that I am obliged to unite with it T. Cummgi, Reeve (Conch. 

 Icon., pi. vii, figs, la, b), T. ferriiginea, Reeve (Conch. Icon , sp. 8), 

 and T. scapha, Meusch. (Thes. Conch., fig. 16). 



6. T. SERRiFERA, Lamk. (Thes. Conch., vol. v, pi. 489* fig. 17, 

 as var. of T. squamosa). This species seems to stand alone. The 

 beautiful specimen in the British Museum is yellow ; it has no lamellaa 

 or prominent scales, but is serrated near the umbones with a few very 

 small sharp scales. Our specimens from the Philippines are white, 

 smaller, and more compressed. 



7. T. OBESA, Sowerby (Proc. Malac. Soc, vol. iii, p. 210, 1899). 

 Beyond the three specimen's mentioned of this very distinct species 

 I have as yet seen no others. 



8. Tridacna acuticostata, n.sp. 

 Shell oblong, white, anterior produced, rounded at the extremity, 

 posterior shorter, sloping, and forming at the extremity with the ventral 

 margin a rather acute angle ; byssal orifice large, oblong-acuminate, 

 revealing two short rows of nodules at the posterior end ; ribs about 

 9, angular, distant, surmounted by small, close-set, angular, and 

 noduldus scales, interstices broadly concave, lirate, crossed by stout 



' Spec. Zoolog. Mosambicana, p. 238, pi. iv, fig. 2. 



