4<D TRUE CRABS OF MONTEREY BAY 



Cancer productus Randall. 

 Plate VIII, figs. 20-24. 



Cancer productus Randall, Journ. Acad. Nat. Sci. Phila., viii, 116, 1839. Holmes, 

 Occas. Papers Calif. Acad. Sci., vii, 47, 1900. Rathbun, H. A. E., x, 175, 1904. 



This species is represented by numerous specimens, as it is one of the 

 most common of the large shore crabs of Monterey Bay. Age differences, 

 as noted by various writers, are conspicuous. The most noteworthy are 

 in the relative length and width of the carapace and the width of the front, 

 and as the age differences in this species are in general similar to those 

 of the genus and show of how little value are such specific characters as 

 the proportion of the front to the total width of the carapace, a consider- 

 able series of measurements is given. The frontal and antero-lateral 

 teeth in the adult are more sharply defined and have more acute tips than 

 in the young, and on the other hand the crests on the hand of the young 

 are more acute than those of the adult. Another age difference which I 

 have not seen mentioned is that of the length of the external maxillipeds. 

 In the adult they overlap the endostome to a marked degree, and this has 

 been used as a family character. In the young, however, the maxillipeds 

 are shorter and reach only to the endostome, as is the case with many of 

 the Pilumnidae Xanthias, Cycloxanthops, and others. 



The adult color of a "dark red above, below, a dirty white" or 

 "yellowish white" is not invariable, though there are no striking differ- 

 ences ; some adults show a light red above due to minute red spots, not so 

 numerous as in the case of the darker color, on a yellowish ground. The 

 longitudinal colored lines of the immature specimens as described by 

 Holmes is not the invariable youthful coloration ; various mottled patterns 

 are also found and occasionally the red of the adult. 



The chief sexual difference seemed to be the greater convexity of the 

 female carapace, which is quite marked in large specimens. 



All specimens listed in the following table, except as otherwise stated, 

 are from Pacific Grove. 



The breadth of the carapace was measured at the eighth antero- 

 lateral tooth, the inter-orbital width was measured between the inner 

 supra-orbital fissures ; the convexity was the height of the center of the 

 carapace above the tips of the eighth antero-lateral teeth, and this per 

 cent is calculated on the basis of total width=ioo; all other per cents have 

 the total length as 100 ; owing to the difficulty of measurement, the con- 

 vexity is less reliable than the other measurements. 



