NO. 3652 ISOPODA AND TANAIDACEA—MILLER 31 
divide on the opposite coasts are not exactly comparable. According 
to Dana’s (1852) isocrymal chart, Cape Hatteras lies at the point at 
which the isocryme of 62°F leaves the Atlantic coast, whereas Point 
Conception is about the intercept of the isocryme of 56°F on the 
Pacific coast. Cape Hatteras thus divides the warm Temperate Zone 
waters that extend southward along the Atlantic coast to Cape 
Kennedy (Canaveral), Fla., from the colder temperate waters that 
range northward from it. On the Pacific coast, however, Point Con- 
ception separates the Temperate Zone waters of southern California 
and northern Baja California from the Subtemperate Zone waters of 
the central California coast. Moreover, the warmer coastal waters of 
Florida, the Bahamas, and Gulf coast lie in the Subtorrid Zone 
(bounded by the isocrymes of 68°F and 74°F), but this zone is not 
represented along the Pacific coast of the United States. Although 
the west coast waters south of Point Conception are colder than those 
of corresponding latitudes along the Atlantic coast, the coastal waters 
of the northwest Pacific coast are warmer than those of the New 
England coast. The Subfrigid Zone (bounded by isocrymes of 35°F 
and 44°F) extends as far south as Cape Cod on the Atlantic coast 
but only to the Straits of Juan de Fuca on the Pacific coast. 
The northern Atlantic group comprises Janira alta and Idotea phos- 
phorea plus the widely distributed I. balthica and I. metallica. All these 
were collected from buoys north of Cape Hatteras and are not known 
to occur south of it. 
The southern Atlantic coast species merge with those of the Carib- 
bean and Gulf of Mexico and include: Accalathura species,* Carpias 
bermudensis, Cymodocella species,* Exocorallana subtilis, Paracerceis 
caudata and Skuphonura species,* plus the widely distributed Cirolana 
parva, Sphaeroma walkeri, and Leptochelia dubia. Three of these (aster- 
isks) were found only in the Bahamas. 
Another Atlantic coast species, Sphaeroma quadridentatum, cannot be 
assigned to either northern or southern group as its range extends 
from southern New England to Key West, Fla. In the present study it 
was collected both north of Cape Hatteras in the mouth of Chesapeake 
Bay and well south of it in Florida. As most of its recorded localities 
are south of Cape Hatteras, this species is associated more closely with 
the southern group. 
The northern Pacific group comprises Dynamenella benedicti, 
Gnorimosphaeroma oregonensis, Ianiropsis kincaid. derjzugini, Idotea 
wosnesenskii, Idotea stenops, Synidotea laticauda, Synidotea species, and 
Tanais species. None of these occurs south of Point Conception. Two 
are quite common along the entire Pacific coast north of Point Con- 
ception—Gnorimosphaeroma oregonensis and Idotea wosnesensku. By 
contrast, Synidotea laticauda is restricted to San Francisco Bay. There 
