HORN EXPEDITION—MOLLUSCA. 
215 
Isidopella newcombi, Ad. and Ang., sp. (Plate XIX., Fig. 25.) 
As an aggregate species I. newconhi includes Physa inflata and Physa hrazieri, 
the distinctions between which I’eside in the comparative lengths of the spire. 
In forma tvpica^ as studied in co-types from the original locality, the spire is very 
prominent and the apex is acute. In forma inflata, as studied in specimens from 
the type locality, the apex is obtuse and its two or two-and-a-half whorls are barely 
elevated above the plane of the penultimate whorl. In forma hrazieri, as studied 
in authentic examples from Rylstone, N.S.W., the shape is somewhat intermediate 
between the other two, but its acute apex and less inflated body-whorl link it 
more to forma typica than to forma inflata. The dimensions of the type are—total 
length 12, length of aperture 7‘5, which agree with the specimens obtained by me 
in Hugh River. But examples from the River Darwent have a shorter spire, 
though the last whorl is not so much inflated as forma inflata, and attain a total 
length of 15 mm. and length of aperture of 10, whilst the largest examples measure 
16 and 11. These agree exactly with the short-spired examples associated with 
the typical shells at the original locality. Thus, briefly, forma typica is long- 
spired, forma hrazieri is short-spired, and forma inflata is very short-spired. The 
relative dimensions of axial length of shell and of aperture is stated in the follow¬ 
ing table :— 
Length. 
Aperture. 
Ratio. 
Forma typica 
- 20-5 
12-5 
100 
: 60 
Forma bi'azieri. 
, Rylstone - 12 
7 ‘5 
100 
: 62-5 
R. Hugh 
j a - - 15 
10 
100 
: 66.5 
\h - - 16 
11 
100 
: 69 (vix). 
Forma inflata 
- 15 
11 
100 
; 73 
Forma hrazieri 
merges so gradually into for7na typica that I 
can 
only regard 
the type of Physa hrazieri as a mere individual variation of /. newcombi; on the 
other hand Physa inflata may have some little claim to varietal distinction, as 
though it is approached and even equalled in shape by extremely inflated indi¬ 
viduals of forma hrazieri, yet it seems to retain the depressed spire and the more 
distant ciliate lines characteristic of extreme examples of that so-called species. 
Localities Forma typica. —Storm Creek, Laurie’s Creek, Alice Springs, JMaude 
Creek. Forma hrazieri —River Stevenson, Sullivan’s Creek, Laurie’s Creek, River 
Darwent, River Hugh (north of Brinkley Bluft'). Forma inflata (but spire slightly 
exsei't)—Storm Creek and River Stevenson, mixed with forma newcombi and 
forma hrazieri; Boggy Flat (between Charlotte Waters and River Coyder), River 
Darwent. 
