PART 1 GARTH : PACIFIC OXYRHYNCHA 375 



Habitat: Under stones at low water. (Bell) At low tide under 

 stones and coral. (Lockington) In tidepools among short weed and in 

 Pocillopora coral. (Crane, 1947) Sluggish, tightly gripping, small spider 

 crab found abundantly in interstices of coral. (Steinbeck and Ricketts) 



Depth: Intertidal, with the exception of two stations in the Tres 

 Marias Islands, Mexico, where it was dredged in from 3-5 and 13 

 fathoms, respectively. 



Size and sex: Males in the Hancock series are from 4.6 to 14.8 mm, 

 females from 4.6 to 12.5 mm, ovigerous females from 6.7 to 12.5 mm. 

 Young of from 2.5 to 3.8 mm are commonly cracked from coral heads. 

 Although the largest specimens are from the Gulf of California, a 14.3 

 mm male (the neotype) was obtained at Manta, Ecuador. 



Breeding: Females with ova in August in the Gulf of California. 

 (Lockington) 



Remarks: In synonymizing Mithrax (Mithraculus) areolatus Lock- 

 ington to M. (M.) denticulatus Bell, the writer has been anticipated only 

 by Crane (1947, p. 73) , although Rathbun was earlier aware that this was 

 in order, judging from a pencil note in her hand discovered at the U. S. 

 National Museum. If one were restricted to the Gulf of California and 

 the other to the Bay of Panama, they might be segregated as geographical 

 races or subspecies ; but even the meager records available until recently 

 included stations in the vicinity of Cape San Lucas and Panama for 

 both. Now these widely separated places are connected by a series of 

 stations from intermediate localities, including those of the Zaca as well 

 as the Velero III. There remains only the question of local variation, 

 covered also by Crane, who states that specimens from the same place 

 differ from one another as to the relative advance of the antennal spines, 

 and that individual specimens are sometimes asymmetrical in this respect. 

 The remarkable thing about M . (M.) denticulatus, including also speci- 

 mens formerly referred to M. (M.) areolatus, is not how different, but 

 how much alike are specimens from localities separated by thousands of 

 miles. 



Now that the provenience of Mithrax (Mithraculus) denticulatus 

 is firmly established as the west coast of America from Cape San Lucas 

 (and possibly San Diego) to Ecuador, it seems timely to dispose of the 

 question of type locality. To begin with, of 850 specimens of Mithrax 

 (Mithraculus) collected by the Velero III at 57 Galapagos stations, all 

 were the endemic M. (Mithraculus) nodosus, and not one the mainland 

 M. (M.) denticulatus. Moreover, no M. (M.) denticulatus were ob- 

 tained at Clarion or Socorro islands, either by intertidal collecting or 



