36 TRUE CRABS OF MONTEREY BAY 



As considerable interesting material was available in this genus I 

 have included as far as possible all the species found on this coast in the 

 keys : specimens of all of which with the exception of amphioehis have 

 been examined. For six species — productus, jordani, gracilis, gibbosulus, 

 antennaritis, and anthonyi — sufficient young material was at hand to 

 render possible the identification of immature specimens down to a size, 

 in most cases, of 5 mm. in width. A key is given for those measuring 

 20 mm. and less in width, as the key to adults will not hold in many cases 

 for the young and it is often very desirable to be able to place immature 

 specimens, some of which are very liable to confusion with the adults of 

 smaller species. Satisfactory identification of small forms will not be 

 possible in all cases without material for comparison ; in fact the young of 

 several species could be placed only through a complete growth series, a 

 study of which disclosed some very interesting facts. 



Although gracilis and gibbosulus differ so widely in the adult or even 

 in specimens measuring 20 mm., at a size of 5 mm. they are almost in- 

 distinguishable, the young of gracilis showing the alternately large and 

 small antero-lateral teeth and a well developed tenth tooth, both of which 

 characters are absent in the adult of this species but present in the adult — 

 and young — of gibbosulus. The case of anthonyi and jordani is similar, 

 here the young of anthonyi exhibit many of the characters of the adult 

 jordani. 



It is of course unsafe to rely too much upon the recapitulatory 

 nature of these ontogenetic resemblances, but if even the slightest value 

 is allowed them some very interesting light is thrown on the relationships 

 of this group, promising much to a more extended study. The young of 

 the six species mentioned, with the exception of productus, show many 

 characters in common; they are pubescent, the antero-lateral teeth are 

 alternately large and small and have spiny tips, the antennas are large, 

 stout and hairy, the chelipeds are more or less spiny, the carapace is long 

 in proportion to its width,and the front is proportionally very wide. Some 

 of these characters, such as the greater length of the carapace and the 

 prominence of the front, are undoubtedly connected with the metamor- 

 phosis from the larval form, but others, for instance the alternately large 

 and small teeth, which at least in gracilis appear immediately on molting 

 from the megalops stage, seem hardly to be in any way connected with 

 the metamorphosis or other ontogenetic changes. Of these five species 

 only two — jordani and gibbosulus — retain the above mentioned characters 

 in the adult, but here they are well marked. (See figures of these species.) 

 Now gibbosulus was the type of the genus Trichocarcinus, and these 



