178 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.24 



Measurements: Males, 3.2 to 7.3 mm; ovigerous females, 5.5 to 8.3 

 mm. The male holotype is 6.3 mm long, 5.7 mm broad. Measurements 

 of the 14 specimens from Cabo San Lucas were not recorded. 



Color: In alcohol, pale reddish orange, the color a little darker on 

 the granules and tips of the fingers. 



Ecology: All the Hancock Foundation specimens were collected 

 under stones in the littoral zone; so, presumably, were those taken at 

 Cabo San Lucas by John Xantus. All females collected in January and 

 February of 1954 were ovigerous. 



Relationships: Clastotoechus diffractus is not analogous to either 

 of the Atlantic species. It differs from both of them in having a more 

 strongly granulate and rugose carapace, and in having the brush of hair 

 on the outer margin of the manus characteristic of females only. In C. 

 vanderhorsti the front and orbits are similar in form to those of C. 

 diffractus, but the frontal lobes are markedly elongate; the carpal teeth 

 are narrower in proportion to their breadth than in either C. diffractus 

 or C. nodosus. The latter species differs from the other two in having 

 the lateral lobes of the front pointed instead of truncate, and the orbits 

 rounded instead of oblique. 



Remarks: Clastotoechus diffractus is apparently a rare species. In 

 spite of extensive collecting along the Mexican Pacific coast over a 

 period of many years, only 23 specimens from three stations are known 

 to date; it was described as recently as 1957. The species probably 

 does not occur within the Gulf of California, or it would certainly have 

 been taken during the intensive collecting carried on in that area. 



Range: Known only from Cabo San Lucas at the mouth of the Gulf 

 of California, south to Acapulco, Mexico. 



ALLOPETROLISTHES, new genus 

 Type species: Porcellana angulosa Guerin, 1835. 



Carapace rounded, approximately as broad as long. Front trilobate, 

 two supplementary lobes sometimes present. Eyestalks short and stout, 

 retractile. 



Basal segment of antenna somewhat produced forward and narrowly 

 in contact with outer orbital angle, thereby slightly excluding movable 

 segments from orbit ; strongly produced inward and, with the inner side 

 of the basal segment of the antennule, forming a complete or nearly 

 complete suborbital margin. Movable segments tuberculate. 



