8 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 125 
species probably have developed as a consequence of long geographic 
or ecological segregation of populations. There is also the possibility 
of hybridization between related alien and native species. Misidenti- 
fications, of course, distort the distributional picture; hence, authors 
should indicate the uncertainties in their determinations and their 
reasons for them. Such information also is valuable in systematic 
revision. 
Group Hemibranchiatae 
Sphaeroma quadridentatum Say 
FIGURE 3 
LocauitiEs.—Virginia: near Norfolk (Stations 32, 33). Florida: 
Tampa Bay (Station 52). 
Remarks.—Richardson (1905b) lists Sphaeroma quadridentatum 
from many localities along the Atlantic seaboard from southern New 
England to Key West, Fla. Intermediate collection sites include waters 
in the vicinity of Cape Charles City, Va.; St. Catherine Island, Ga. 
(type-locality) ; and Beaufort, N.C. The buoys from which this species 
was collected lie within its known range. The available ecological data 
indicate that the species prefers muddy bottoms. 
Nierstrasz (1917) reported this species from the Mediterranean, 
but Monod (1931b) lists the Mediterranean forms in the synonymy 
of Sphaeroma serratum (Fabricius) H. Milne Edwards. Earlier, Monod 
(1930) following Torelli (1930), also had equated S. quadridentatum 
from the east coast of North America with S. serratum. After examining 
topotypes of the former, however, he concluded that the two were 
separate species. He pointed out the following three distinctions: (1) 
In S. quadridentatum, there are four well-defined teeth on the outer 
border of the uropodal exopod, whereas the number of teeth varies in 
S. serratum (occasionally four) and they are often irregular crenula- 
tions, making it difficult to determine the precise number. (2) The 
posterior part of the telson in males of S. quadridentatum tends to be 
excavated dorsally with upturned borders, while in S. serratum it is 
vaulted more regularly. (3) In S. quadridentatum, there are fewer setae 
in the distal row on the propodus of pereopod I than in S. serratum. 
The buoy specimens confirm these observations. 
Sphaeroma walkeri Stebbing 
FIcurE 3 
Locatities.—Florida: Ponce de Leon Inlet (Station 36), Sarasota 
New Pass (Station 49), Egmont Channel (Station 51). Hawaii: Hilo 
(Station 97). 
ReMARKS.—Previous reports indicate that Sphaeroma walkeri is 
widely but spottily distributed as follows. India: Gulf of Manaar 
(Jokkenpidd: Parr, Marichchukaddi, Cheval Paar, and Galle Harbour, 
