20 



CONCHOLOGIA INDICA. 



PLATE XLIII. 

 UNIO. 



1. U. Thwaitesii, Lea, Proc. Philad. Ac. N.S. vol. 1 

 (1859), p. 152 ; J. Philad. s. 2, vol. 4, pi. 37, 

 f. 125. — Eeeve, Concli. Icon. Uuio, f. 105. 



Ceylon. 



U. marginalis, Lamarck, Anim. s. Vert. ed. Desh. 

 vol. 6, 15. 544. — Hanley, Rec. Bivalves, p. 206, pi. 

 19, f. 53. — U. testudinarius, Spengler, Skriv. Nat. 

 Selks. vol. 3, pt. 1, p. 65, and U. truncatus, p. 56 

 (fide Bliircli). — U. Grronlandicus (in Lea) from 

 Scbruter, Fluss. Conch, p. 181, pi. 9, f. 1. 



We describe the hinge of the typical form, which is 

 but little modified in any of the varieties. In the right 

 valve are two sloping anterior teeth, of which the 

 upper and narrower arches more or less downwards, 

 and tlie lower is strong and rather large ; the single 

 lateral one is strong, elongated, and bent at the end. 

 In the left valve, besides the callus, there is one ante- 

 rior and two lateral teeth, the latter scarcely divided 

 until the second moiety, where they slant down. The 

 principal anterior scar is decidedly large in proportion 

 to its size in the allied species. After long examina- 

 tion of many scores of examples of this most variable 

 species from nearly every part of British India, we can 

 only arrive at the conclusion that the forms usually 

 designated in cabinets, bilineatus, lamellatus, Corrianus, 

 &c., all run into each other. We do not assert, how- 

 ever, that the shells intended by Lea are identical ; for 

 his figure of bilineatus looks like the young of some 

 broadly-winged Siamese shell (of the Housei type), and 

 his lamellatus is notable for a peculiarity of dentition. 

 We have delineated some of the more striking forms. 



2. U. marginalis, var. typica. — U. marginalis, En- 

 cycl. Meth. Vers, pi. 247, f. 1. 



Moradabad : Pegu. 



The brief Lamarckian diagnosis is further defined 

 by his reference, &c., and his figure. 



3. U. marginalis, var. obesa. 



River Irawadi, Birmah. 



A giant form, which does not exhibit the ochraceous 

 band, and is peculiarly swollen. It comes between the 

 var. lata, and the typical form. The upper anterior 

 tooth is almost linear ; the lateral are not bent at the 

 extremity, and the upper one in the left valve is 

 scarcely developed. 



4. U. marginalis, var. Candaharica, Button, J. 

 Asi. Soc. Beng. vol. 17, pt. 1 (1849), p. 651. 

 River Sutlej. 



The abnormal characters of shajie and colouring are 

 such that Hutton (its discoverer) suggested its possible 

 distinctiveness. The nucleus very closely approaches 

 U. theca, Benson ; the adult cannot be sejjarated from 

 the form bilineatus. 



5. TJ. marginalis, var. tricolor. — U. tricolor, Kuster. 

 ed. Chemn. Unio, pi. 45, f . 1 ? 



A very beautifiilly painted shell, which is usually 

 more or less comjjressed. 



PLATE XLIV. 

 UNIO. 



1. TJ. marginalis, var. cylindrica. 



2. U. marginalis, var. zonata. — U. marginalis, Desh. 

 Encycl. Meth. Vers, vol. 2, p. 587. 



Belgaum, Deccan. 



3. U. marginalis, var. bilineata. — U. bUineatus, 

 Reeve (as of Lea), Conch. Icon. Unio, f. 365. 



Nearly all the varieties (especially the immature 

 examples) exhibit two raised lines near the beaks on the 

 umbonal slope. We are aware that Spengler intended 

 to have indicated U. marginalis as U. testudinarivis, 

 but his Latin description is most utterly inadeijuate to 

 define it ; his delphiuus, conus, and gibbosus (from the 

 East Indies), must be ignored for a similar reason. 

 The name Grajnlandicus (the locality was subsequently 

 corrected in the Einleitung, vol. 2, p. 621, by Schroter 

 himself), would mislead. 



4. U. marginalis, var. Corriana. — U. Corrianus, Lea, 

 Trans. Amer. Phil. Soc. vol. 5, p. 177, pi. 9, f 25, 

 from which Hanley, Rec. Bivalves, p. 207, pi. 21, 

 f. GO. 



Near Calcutta, &c. 



This form, always more or less indented in the middle, 

 is sometimes elongated cylindrical, sometimes com- 

 pressed and oval-oblong. The cardinal callosity (rarely 

 absent) is more or less developed, and the anterior or 

 hinge teeth are almost horizontal, curve outward, and 

 are either rather elongated, or if shorter, are rather 

 prominently elevated. 



