so CONTRIBUTIONS FOR SYSTEMATIC CATALOGUE AQUATIC SHELLS. 



Truncatella. It is of a still more slender form, tliau as shown 

 in the illustrations, which represent some as of a very 

 compressed nature. 



Kydrohia Gunnii. V. Frfld, this was already described 

 amonfjst the number and siiocies of these shells in the 

 Transact, of the K. K. Zool. and Bot. Soc., 1833, page 1,025, 

 also in same Transact., page 612, No. 387, 1864." 



Amnicola diemense, Frfld. 



" Transact, of the Iv. K. Zoological and Botanical Society, 

 Vienna, Vol. XIII. No. III. and IV., page, 3,028, 1863. 



In Mr. Cummiugs ' collection from Van Dieraen's Land, this 

 is represented (as intermingled with Hydra Gunnii, Frfld. 

 and cristallina Pfr.) This shell is acute, conical, brownish in 

 colour, almost non-transparent, 4| turns or windings, slightly 

 arched, and gradually becoming more so towai-ds lower 

 extremity, last whorl largely developed. The mouth is almost 

 circular, large down to half of the length of the shell, edge 

 somewhat wider, not clinging to whorls ; umbilicus distinctly 

 visible and deep. 



Laigi/i, 2" 7 nun. 7i>idth, 1-9 mm. There were several 

 specimens much smaller, slender, and obtuse, with smaller 

 orifices, so that it was difficult at first to classify between 

 these extremes, though, at last I discovered a medium by 

 means of which these difficulties were put aside. 



Note. — I am not quite certain whether these species could 

 not be more properly designated with Hydrohia, Frfld. 



Hydrobia cristallina. Pfr. 



2. Van Diemen's Land, Mr. Gunn ; intermingled as afore- 

 said with Hydrobia Gunnii Frfld and Amnicola dienufise Frfld. 

 As referred to in the Transact, of the K. K. Zoology and 

 Botanical Societv, Vienna. Vol. XIII. No. III. and IV. 

 Page, 1,024. 1863." 



Atnnicola diemense. V. Frfld. 



" Transactions K. K. Zool. and Bot. Soc. Vol XV. Page 

 520, 1865, pi. X. fig. 2. 



At the same i)lace the shell described as A. floridana V. 

 Frjld., I nob.'d that it was not quite sure whether or not these 

 two species were not to I)e better incor]»orated with Jlydrobia. 

 In these cfises where the shells are so similar in form, it is 

 often very difficult to decide such a question, and it requires 

 some skill to do so. 



In the next following newly discovered species, it a]>pear3 

 that the slightly compressed forms, the graduated windings 

 or turnH, the more (jp<'n umbilicus, the larger lower mouth or 

 orifice, decided me to classify same as Amnicola, which differs 

 but little from Jfydrobia, and it doubtless renders this classi- 

 fication as very delicate under the circumstances. 



