12 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 125 
authors despite Miss Richardson’s stout defense for its distinctness. 
Her S. peruvianum from honeycombed wood in oyster beds in Peru 
and her S. retrolaevis from Japan are regarded as distinct from but 
closely related to S. terebrans. 
As isopods of this species commonly are found burrowing in decayed 
wood, bridge and wharf pilings, dead mangrove roots, etc., dispersal 
by ships and driftwood seems a likely explanation for its widespread 
distribution. As with other widely distributed species, geographic 
and/or ecological segregation may result, in time, in reproductive 
isolation of local populations and subsequent speciation. 
The specific identification of the Texas specimens is questioned 
primarily because the sculpturing of the dorsal surface, as far as this 
can be determined, does not conform entirely to the descriptions of 
this feature in S. terebrans. According to the descriptions, the dorsal 
surface on the posterior part of the body is covered with granules and 
tubercles of various sizes, the larger ones of which bear tufts of 
minute hairs, and there are tuberculated transverse ridges on the 
posterior thoracic segments. Well-developed paired tubercles are said 
to be characteristically present on the last one or two thoracic and 
on the two pleonal segments. The literature indicates, however, a 
certain amount of variation in sculpture pattern as well as in other 
characteristics. 
Considerable individual variation in tuberculation was observed 
in the Texas specimens. The smaller ones were smooth, as in S. 
quadridentatum, or only minutely granular and transverse thoracic 
ridges were only slightly evident. Larger specimens usually were 
coated with mud, especially on the hinder part, which obscured the 
tubercles. Several previous authors mentioned the same difficulty 
with mud. In our specimens, the coating adhered so tightly that, 
when attempts were made to remove it, the underlying exoskeleton 
also peeled off. Nevertheless, it was possible to observe that our 
specimens had finely tuberculated transverse ridges on the posterior 
thoracic segments and tubercles on the pleon and pleotelson. Some 
specimens showed large paired tubercles on the pleon, others did 
not, and the pattern was not consistent. In some, there was evidence 
of two paramedian rows of tubercles on the pleotelson, as in S. quoyana 
M. Edwards. 
Gnorimosphaeroma oregonensis (Dana) Menzies 
FIGURE 3 
Locauitirs.—California: San Francisco Bay area (Stations 74-78, 
80, 84-87, 91). Washington: Umatillo (Station 95), Quillayute River 
(Station 96). 
Remarks.—This species, first described by Dana (1852) as Sphae- 
