16 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 24 



types were part of this series of 35 specimens, but the U. S. National 

 Museum holotype and paratype, and the San Diego Museum paratypes, 

 were labelled without the Santa Margarita Island designation. An un- 

 identified lot of 12 specimens in the U. S. National Museum collection 

 is labelled "Magdalena Bay, B. C, 12/4/31, 1 fathom, Margareta Is., 

 S. A, Glassell." It is believed that these specimens may also be a part 

 of Glassell's original series, and that the date December 4 is an error 

 for December 2. 



Although the species has not been mentioned in the literature since 

 its description in 1936 from a single locality, the present study shows 

 that it ranges throughout the Panamic Province. Its very small size and 

 restricted habitat probably account for its scarcity in collections. 



Range: Bahia de la Magdalena, Baja California, and Mazatlan, 

 mouth of the Gulf of California, south to Bahia de Caraquez, Ecuador. 

 Shore to about 5 fathoms. 



LIOPETROLISTHES, new genus 

 Type species: Porcellana mitra Dana, 1852. 



Carapace subovate, usually slightly longer than broad. Front strongly 

 produced beyond eyes, trilobate. Eyestalks short and stout, retractile 

 behind supraorbital margin. 



Basal segment of antenna not produced forward to meet anterior 

 margin of carapace; with a long, narrow, acute projection, directed in- 

 ward and, with the outer portion of the basal antennular segment, form- 

 ing a complete suborbital margin. First movable segment very short, 

 nearly concealed behind hepatic margin. 



Basal segment of antennule broad, laterally expanded, with two long, 

 narrow lobes on inner side of anterior face. 



Chelipeds small in relation to carapace, weak, flattened; anterior 

 margin of carpus armed with prominent teeth. 



Walking legs of moderate length, flattened; propodus with mov- 

 able spinules on posterior margin; dactylus ending in a simple spine, 

 with small movable accessory spinules on posterior margin. 



Telson of abdomen composed of five plates. 



Contains a single species. 



Remarks: Liopetrolisthes mitra has most often appeared in the liter- 

 ature as a Porcellana. There is a superficial resemblance to typical 



