NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 71 



small brownish spots. The anal opening has folded margins which seem 

 to form a short siphon. The gonads are dorsal. 



Holotype: Allan Hancock Foundation. Length, 21 mm; height, 10 mm; 

 diameter, 6 mm. 



Type loc: 409-35, Isla Gorgona, Colombia; 20 fms. 

 Remarks: This species is very close to Amygdalum beddomei Pettard 

 (Iredale, 1924, p. 197, PI. 35, fig. 21). The posterior margin, however, 

 is more truncate in Amygdalum americanum and does not show the long, 

 rounded posterodorsal curve which seems to be typical in A. beddomei. 

 The darker markings are also different, according to Iredale's figure. 

 Lamy (1936) records Modiolus (Amygdalum) arborescens (Chemnitz) 

 from Payta, Peru; but it seems reasonable that Lamy had specimens of 

 Amygdalum americanum, as there is no other record of Modiolus arbores- 

 cens from the Pacific coasts of America. Two examples of this species 

 from Bahia de Manzanilla are preserved in the San Diego Museum of 

 Natural History. 



Occurrence: This species seems to prefer shallower water than does 

 Amygdalum pallidulum, as it is taken alive between 2 and 20 fms, on 

 muddy or sandy bottom. There were no traces of a nest like that of 

 A. pallidulumj but a nest is easily lost during the sifting of the material. 

 Distribution: Recorded from Bahia Tenacatita, Mexico, south to Isla 

 Gorgona, Colombia, or Payta, Peru (Lamy). 



Genus LIOBERUS Dall 1898 



Lioberus Dall, Trans. Wagner Free Inst. Sci., vol. 3, part 4, 1898, p. 805. 

 Type of genus: Modiola castanea Say 1822 (orig.). 

 Remarks: Dall's diagnosis is short. As a group (section or subgenus) of 

 Modiolaria Beck, the following diagnosis is given : "Shell with the radial 

 sculpture obsolete or absent; branchial siphon equal or nearly equal to 

 the anal, both much elongated." 



Though the form and smooth surface give the shells a superficial 

 resemblance to Modiolus, the long siphons show that the group has other 

 afHnities. It seems safest to treat the group as a separate genus until more 

 is known of the relationship to the genus Musculus Roding. 



Lioberus castaneus (Say) seems to be at least superficially like some 

 other species usually referred to Modiolus, e. g., Modiolus elongatus 

 (Swainson) (cfr. Pelseneer, 1911, p. 18, PI. 4, fig. 8; PI. 5, fig. 12), 

 which perhaps may be found to belong to Lioberus. Volsella salvadorica 

 Hertlein and Strong is at least tentatively referred to Lioberus because 

 of the anatomy. 



