258 
developing stages of the forma typica, some difference in shape is 
evident. Thus f. inst. carina and rostrum of these young individuals 
of forma echinata are a little more diverging than in forma typica, 
and the siender, pointed shape of the plates is already distinet. 
It is possible that the differences between Gruvel’s statements 
and the present results, spoken of under forma typica (pag- 256) 
are due to a confusion of the two forms here described. My 
material of forma echinata is too small to furnish a base for studies 
of its variations. A study of Nussbaum’s paper (1890) seems to 
reveal that he has had at least both forms before him. Although 
his drawings of the young specimens are inexact, we can see that 
fig. 6 of his pi. I is of a young forma echinata; we thus at pre¬ 
sent are able to State its occurrence at San Francisco, at Lajolla, 
and at San Pedro, California. 
Mitella mitella (Linné) Pilsbry. 
South of Vitalis Point, Mindanao. Coastal rocks. 7/III 14. Some few 
specimens. 
Curiously enough, Gru vel (1905) has not emphasized the most 
characteristic feature of this elegant Mitella, viz. the enormous dev- 
elopment of the upper latus, as compared with the other latera 
(Fig. 20). This feature indeed so strongly contrasts with the other 
species of the genus that we may say that Mitella mitella is char- 
acterized by this feature alone. Because of this character the spec¬ 
ies moreover holds an intermediate position between the pollicipes- 
group [Mitella pollicipes (Gmelin), Mitella elegans (Lesson), and 
Mitella polymerus (Sowerby)], and the sertus- group [Mitella spinosus 
(Quoy et Gaimard), Mitella Danvini (Hutton), and Mitella sertus 
(Darwin)]; the pollicipes-group is characterized by the higher dev- 
elopment of at least upper, carinal, inframedian, and rostral latera; 
in the sertus- group all the latera are uniformly developed, and 
spine-like. — Besides the extraordinary development of an upper 
latus Mitella mitella presents a rich sculpture of the capitulum 
plates. 
I am not able to agree with Gru vel who States the scales of 
the peduncle to be more irregularly arranged in Mitella mitella 
than in Mitella elegans. All specimens which I have had the op- 
portunity of examining, exhibit an absolutely regular arrangement 
