220 
PACIFIC SCIENCE, VoL VIII, April, 1954 
by Kato (1944: 298-302) as Japanese may 
perhaps be regarded as belonging in the 
fringes of the Indo-Padfic region. This is 
certainly true of some of the localities on 
Kato’s list. Thus, well over half the described 
species belong to the Indo-Pacilic area, and 
this area has certainly not been thoroughly 
collected for polyclads. Outside this area, the 
various species appear to have a limited dis- 
tribution as each region furnishes different 
species, except for P. splendidus, reported from 
the Mediterranean, Bermuda, and Puerto 
Rico. Within the Indo-Pacific area, species 
apparently may range widely. 
The genus Pseudoceros is easily recognized 
by the combination of a ruffled pharynx, mar- 
ginal tentacles as upfolds of the anterior mar- 
gin, and an anastomosed intestine that origin- 
ates by many branches from the main intestine. 
If the species with small papillae over the 
dorsal surface are to be separated as a distinct 
genus, then the possession of a smooth dorsal 
surface becomes another character of Pseudo- 
ceros. Contrasting with the easy recognition 
of the genus is the great difficulty of separat- 
ing the species; they are very similarly con- 
structed, and the color pattern, which is often 
very striking, becomes almost the only means 
of distinguishing them. Preserved specimens 
not accompanied by color notes are almost 
impossible to identify. However, even with a 
full knowledge of the color pattern one is 
often puzzled to know whether the color cor- 
respondence with a described species is suffi- 
ciently close or not. Little is known of color 
variation in the genus except that some species 
are described as showing considerable color 
variation. Therefore, other possible identify- 
ing characters should not be neglected in a 
specific description in the genus, especially 
the details of the copulatory apparatus. Al- 
though the reproductive system, too, is very 
similarly constructed throughout the genus, 
minor differences are evident in the copula- 
tory apparatuses and often prove helpful in 
species discrimination. The difficulties of spe- 
cies discrimination on the basis of color alone 
will be evident in the following account. 
Pseudoceros bedfordi Laidlaw, 1903 
This species was originally described (Laid- 
law, 1903: 314) from a defective specimen 
taken at Singapore. Later, Bock (1913: 254) 
came into possession of a perfect specimen 
collected off Billiton on the island of Min- 
danao in the Philippines. Bock’s specimen 
was 35 millimeters long by 20 millimeters 
wide. He gave an excellent figure showing the 
very distinctive and unmistakable color pat- 
tern and also verified the paired condition of 
the male copulatory apparatus. Subsequently, 
Kato (1943: 87) reported the species as com- 
mon in the Palau Islands, swimming about 
in shallow water. Kato also gave a good figure 
to illustrate the color pattern. His specimens 
were relatively small, ranging from 20 to 35 
millimeters in length and 10 to 20 millimeters 
in breadth. 
The present specimen is a fine, large, per- 
fect example collected at Heron Island in the 
Great Barrier Reef of Australia in the summer 
of 1952. It is the largest specimen on record, 
measuring 60 millimeters in length and 45 in 
width. The color pattern quite agrees with 
the figures of Bock and Kato. On a purplish- 
brown ground (described by previous ob- 
servers as greenish black or dark brown) are 
found numerous arcs and dashes of a buff 
color, distributed irregularly but in a bilateral 
pattern over the dorsal surface. 
The specimen has been deposited in the | 
American Museum of Natural History. The ! 
species is evidently widely spread throughout ! 
the Indo-Pacific area. | 
Pseudoceros concinnus (Collingwood) ji 
1876 j 
Fig. 1 ' 
Proceros concinnus Collingwood, 1876: 90, pi. j 
17, fig. 4. || 
Several specimens, assigned with some re- 
serve to this species, were presented to me 
by Dr. A. G. Humes, who collected them on 
