20 
PACIFIC SCIENCE, Vol XXI, January 1967 
description: In lateral view: dorsal margin 
sinuous; anterior margin truncate; ventral mar- 
gin straight, parallel with dorsal margin, curv- 
ing up posteroventrally about 45° to high 
pointed posterodorsal caudal process; oblique 
posterior margin finely and evenly denticulate. 
Carapace fragile, small; alar processes large, 
running from ventral part of anterior margin 
out and back at about 30° to greater than half 
the length of carapace; dorsal ridge knobby 
from pointed posterodorsal caudal process to 
anterior margin; grotesque tubercle just ante- 
rior to deep vertical central sulcus; alae intri- 
cately ornamented with sinuous parallel riblets 
in ventral part developing into many small 
knobs behind alae. 
Hingement lophodont: anterior tooth of 
right valve small, posterior tooth elongate, in- 
conspicuous; median bar of left valve slightly 
extended, crenulate at ends, otherwise appar- 
ently smooth. Duplicature narrow; other inter- 
nal features not observed. 
dimensions: 
SPECIMEN 
LENGTH 
WIDTH 
HEIGHT 
Holotype usnm 648740 
(left valve) T-12 
0.55 
0.22 
0.27 
Paratype sdnh 1041 
(left valve) T-12 
0.54 
0.22 
0.27 
Paratype usnm 648741 
(right valve) T-12 
0.55 
0.22 
0.27 
Paratype USNM 648742 
(left valve) T-12 
0.54 
0.21 
0.29 
distribution: As fossils from T-ll (1 
valve), T-12 (13 valves), S-23 (1 valve), and 
Easter Island at EA-2 (6 valves). 
discussion: This species bears a strong re- 
semblance to two forms from the west coast of 
North America. One occurrence of a form 
strikingly similar to Bythoceratina monstruosa 
has been found by the writer in the Coronado 
Islands 20 miles off San Diego, California. The 
Recent form is almost identical with the fossil 
from Hawaii, but differs by having a serrated 
anterior margin and faint reticulations over 
most of its surface. Another species of Bytho- 
ceratina has been observed by the writer in the 
Pleistocene of Turtle Bay, Baja California, 
Mexico. These three forms share many simi- 
larities and are undoubtedly closely related; 
however, the Turtle Bay form is clearly a dis- 
tinct species. Monoceratina sp. B of Keij 
(1953) is also similar to the new species but 
lacks several details in ornamentation. The 
apparently Recent species of Keij occurs in 
redeposited faunas at 847 and 1,947 fathoms 
in the Celebes Sea, Netherlands East Indies. 
The genera Monoceratina and Bythoceratina 
have not been previously reported from the 
west coast of America. 
Bythoceratina monstruosa, and its North 
American allies, differ from the New Zealand 
species of Bythoceratina (Hornibrook, 1952: 
62-63) in having a smooth median element 
and knobby alae, lacking a hollow ventrolateral 
spine. However, one New Zealand species, B. 
utilazea Hornibrook, 1952, from the Lower 
Miocene to Recent of New Zealand, has close 
affinity to the present species. These two re- 
semble several Upper Cretaceous Monoceratina 
from South Limburg in the Netherlands, viz., 
M. parva, M. pygmaea, M. sulcata, M. pulchra, 
and to a lesser degree M. pseudosulcata, all of 
van Veen, 1936. This group is characterized by 
a dorsally lanceolate shape and the lack of a 
ventral spine. The species is named for its 
grotesque ornamentation. 
Family cytheruridae Muller, 1894 
Genus Paracytheridea Muller, 1894 
Paracytheridea sp. 
Figs. 13 a-b 
dimensions: Specimen usnm 648743 (left 
valve) T-12: length, 0.31; width, 0.15; height, 
0.14. 
distribution: As fossils from T-12 (2 
valves) . 
discussion: Poor preservation and lack of 
material do not warrant a detailed treatment 
of the present species. It is possible that the 
figured specimen, the larger of the two, is a 
young one, although some species of this genus 
are not much larger (Morkhoven, 1963:378). 
Family hemicytheridae Puri, 1953 
Genus Hemicythere Sars, 1925 
Hemicythere obesa n. sp. 
Figs. 14 a—d 
diagnosis: Large smooth inflated carapace; 
straight subparallel ventral and dorsal margins ; 
