California Xanthidae—KNUDSEN 
5 
is 25 per cent or less than the length of the 
third abdominal segment; ( 3 ) the sixth abdom- 
inal segment is narrower than the second in 
young, but immature females; (4) the pleopods 
are sparsely provided with "hairs”; and ( 5 ) the 
lock mechanism is present. The lock mechanism 
is typical of male crabs of this species, and con- 
sists of a pair of cup-shaped pockets on the 
distal-lateral margins of the sixth abdominal seg- 
ment, and a pair of protuberances projecting 
forward from the fifth thoracic sternite which 
lies in union with the sixth abdominal segment. 
When the abdomen is "closed,” the cups of the 
sixth segment fit over the protuberances of the 
sternite and serve to lock the abdomen in place. 
The last abdominal segment is free, and is ex- 
tended for defecation without lowering the en- 
tire abdomen. The protuberances of the sternite 
are the most conspicuous evidence of this mech- 
anism. Generally the maximum carapace width 
of the immature female is 28.5 millimeters. 
Submature or transitional females have well- 
developed ovaries but generally lack developing 
ova. The morphological changes from the pre- 
ceding stages are as follows: (1) abdominal 
segments three and four are of nearly equal 
width; (2) the lateral "hair” on the sixth seg- 
ment is almost 50 per cent as long as the third 
abdominal segment; ( 3 ) the pleopods are more 
fully developed; and (4) the lock mechanism is 
generally present. The size of this stage ranges 
between 28.5 and 33.0 millimeters. 
The fully mature female Cycloxanthops no- 
vemdentatus is about 33.0 millimeters wide or 
wider, and has fully developed, gravid ovaries 
(in season). Externally these specimens can be 
determined by the following features: (1) ab- 
dominal segments four and five are the widest; 
(2) the lateral "hair” of the sixth segment is 
about equal in length to the third abdominal 
segment; (3) the sixth segment is wider than 
the third; (4) the pleopods are very full in ap- 
pearance; (5) the lock mechanism is lacking 
entirely; and (6) the groove in the sternum 
occupied by the abdomen is proportionally shal- 
lower and wider than in the immature or male 
condition. 
About 4 per cent of the females examined had 
a carapace width of 19.2 to 21.5 millimeters, but 
had all of the characteristics of a mature female. 
Normally female Cycloxanthops novemdentatus 
are not ovigerous until June in southern Cali- 
fornia, and the individual young take about the 
same length of time to develop, probably two 
years. The small but mature females are prob- 
ably hatched early in April, and thus are large 
enough in the following year to be influ- 
enced by the warm temperatures of late summer. 
Hence, the secondary sex characteristics are 
brought on abnormally early. 
Hiatt (1948: 198) used the presence of 
sperm in the vas deferens as a criterion of matu- 
rity in male Pachygrapsus crassipes. The writer 
examined preparations from 15 Cycloxanthops 
novemdentatus, several other xanthid crabs, and 
several Pachygrapsus crassipes (within the ma- 
ture size range), but concluded that the poor 
results obtained were not worth the destruction 
of additional specimens. A study of the external 
genitalia of the male, however, reveals that the 
intromittent organs are capable only of anterior- 
posterior movement. Thus successful copulation 
could not occur except with equal-sized females. 
In this species the intromittent organs are fully 
developed when the individual is 19.5 milli- 
meters wide. Just prior to this they appear nor- 
mal but are shorter than normal. Thus 20- 
millimeter males are able to copulate with small, 
mature females. However, the fertility of males 
in this size-class has not been established. 
Paraxanthias taylori: The anatomical features 
important in determining the maturity of this 
species are the same as for Cycloxanthops no- 
vemdentatus. Signs of sexual dimorphism are 
seen in 6.5 millimeter specimens when the distal 
abdominal segments of the female begin to 
broaden with respect to segment three. There is 
no clear-cut transitional or submature class, in 
that the morphological features of such a class 
in this species are too indefinite to be of value. 
Immature females which have underdeveloped 
ovaries are characterized by the following ex- 
ternal signs : ( 1 ) the third abdominal segment 
is the widest; (2) the second abdominal seg- 
ment is wider than the sixth segment; ( 3 ) the 
lateral "hair” on segment six is one half or 
less the length of the third abdominal segment; 
(4) and the lock mechanism is always present. 
Females of this species mature between the 
sizes of 11.5 millimeters to 13.5 millimeters. The 
