Some Opisthobranchiate Mollusca from Hawaii 1 
Jens Mathias Ostergaard 2 
INTRODUCTION 
In the attempt to advance our knowledge 
of the marine Mollusca of the Hawaiian Is- 
lands, groups provided with a shell have been 
among the first to receive attention. Largely 
for this reason gastropods of the order Proso- 
branchiata, having conspicuous shells, have 
become better known than have such forms 
as belong in the order Opisthobranchiata, in 
which a shell is often absent in the adult. 
Such nonshelled forms present difficulty of 
adequate diagnosis for the establishment of 
taxonomic characters, inasmuch as the pre- 
served animal soon loses its colors, partly or 
completely, and becomes in some way dis- 
torted because of the contraction of various 
anatomical parts. 
Since the works of Gould (1852) and Harp- 
er Pease (1860-1872), nothing appears to have 
been added to our knowledge of these ani- 
mals in the Hawaiian area. 
The present work is but a small part of 
what needs to be done in this large group of 
mollusks, which is well represented in Hawaii. 
Only those forms whose generic position has 
already been established are dealt with here. 
No dissection has been attempted, and spec- 
ific characters have been based on external 
features only. The colored figures, as well as 
1 Contribution Number 55, Hawaii Marine Labora- 
tory. Manuscript received October 30, 1951. 
2 Department of Zoology and Entomology, Uni- 
versity of Hawaii. 
those in black and white, have been repro- 
duced from the author’s water-color drawings. 
The holotypes of all new species are de- 
posited in the United States National Mu- 
seum, paratypes and other specimens cited 
are in the Bernice P. Bishop Museum, Ho- 
nolulu. 
Acknowledgments: For his fine aid rendered 
over a long period of time in securing speci- 
mens for me, I am very grateful to Dr. Charles 
H. Edmondson. I am thankful to Otto Dege- 
ner for many interesting specimens. During 
the last 2 years, while preparing this manu- 
script for publication, I received from Mr. 
Charles Cutress of the University of Hawaii 
many specimens of opisthobranchiates, for 
which I am very appreciative. Mr. Spencer 
Tinker, director of the Honolulu Aquarium, 
has rendered me valuable services by retaining 
for me many fine specimens of nudibranchs. 
For the aid in taxonomic problems so gen- 
erously given me by Dr. Frank M. MacFar- 
land, I feel a sincere appreciation. Finally, I 
must express my deep gratitude for the aid 
rendered and interest shown in this under- 
taking by Dr. Robert W. Hiatt, director of 
the Hawaii Marine Laboratory. 
KEY TO INCLUDED GENERA OF HAWAIIAN 
Opisthobranchiata 
I. Respiratory organs, when present, con- 
cealed under mantle or attached to right 
side of body or consisting of respiratory 
110 
