SrEI.FOX : PISIDIUM I^AUNA OK THE GRAND JUNCTION CANAL. 299 



proportionately larger appendiculae are the chief external characters 

 1))' which young P. supiman may be separated from P. parvuluni ; 

 the relative position of the appendiculce is another point ; while the 

 mature aspect o( P. parvuhim and the immature appearance of P. 

 siipinuvi of similar size will strike the naturalist's eye at once, though 

 such features cannot be put into words, translated into drawings, nor 

 observed under the microscope. Interiorly, the well-developed liga- 

 ment pit of P. supiimvi^ as well as the larger cardinals, differ appre- 

 ciably from those oi P. parvidum, while/. /// in the former species 

 does not curve inwards to meet /. / as it does in P. parvulum. In 

 the National Museum, Dublin, there are shells sent by Westerlund 

 as "/'. parvulum Clessin," from near Ronneby, Sweden, one of the 

 original localities for the species (see AVesterlund, loc. at., p. 553). 

 These specimens do not resemble the species under consideration, 

 which, however, is conspecific, in my opinion, with that figured by 

 ]\Ir. Woodward in his Catalogue as the P. parvulum of Clessin, and 

 with Danish specimens under this name, k'indly sent to me by Mr. 

 Woodward in 1915. If in future, therefore, it were found necessary 

 to drop the very appropriate name of parvulum for this species, 

 another suitable one might be found in torquahan, derived from the 

 little collar-like appendicular ridge which surrounds the nepionic 

 shell in nearly all examples I have seen. This last feature is omitted, 

 strangely, from both Mr. Woodward's description of this shell and 

 from the original diagnosis of Clessin's species, published by Wester- 

 lund {loc. cif.). 



P. supinum A. Schmidt. Plate 7, figs. 14-18. Also plate 8, figs. 

 3 and 22-25. 



Abundant in the canal at many places. All the specimens are 

 much thickened and acutely triangular in outline when fully grown. 

 This shell may be distinguished from P. casertanum var. ponderosa by 

 its appendiculas, its wider, more strongly marked striation, and intern- 

 ally by its longer, straighter, and narrower ligament pit. From P. 

 tiitidum var. crassa it may be known by its less equilateral shape, its 

 larger cardinal teeth, its simple tube-like siphon, by the presence of 

 appendiculas, and by its less glossy appearance, and different striation. 

 The young of this species may be distinguished from mature examples 

 of P. parvulum by the position of the appendiculte in relation to the 

 rest of the shell, as well as by their different shape and larger size. 

 In young supinum the cardinal c. j is larger, the ligament pit is more 

 strongly marked, straighter, and longer, while exteriorly the shell is 

 much more widely and coarsely striate than in P. parvulum. 

 P. henslowanum (Sheppard). Plate 7, figs. 19-23. 



Alone of all the Pisidia in the canal, this remains for some obscure 

 reason without a thickened shell. A very remarkable fact, and one 



