428 THE AMERICAN NATURALIST. (Vor. XXXIX. 
but in other forms (Amphiporus, Cephalothrix) development 
is direct, or is accompanied only by a shedding of the larval 
integument. 
Nearly all species are marine, living under stones, among 
alga, or in burrows in the sea bottom or shore between tides ; 
representatives of a single widely distributed genus (Sticho- 
stemma) live in fresh-water pools, ponds, or rivers, and several 
Species live in moist earth in warm climates ; a few forms are 
commensal, inhabiting the mantle chambers of pelecypods or of 
ascidians, while the members of a single genus (Carcinonemer- 
tes) are truly parasitic, living among the gill plates or egg masses 
of various species of crabs. 
All Nemerteans may be conveniently arranged in four orders, 
comprising more than thirty genera and several hundred spe- 
cies. Of these, 21 genera with 87 species have been recorded 
from the Pacific coast, the Nemertean fauna of that region 
being more abundant and more diversified than in almost any 
other locality of equal extent. 
For convenience in determination, the 87 species at present 
known from the west and northwest coasts of North America, 
from Panama to the Bering Sea and Arctic Ocean, may be 
arranged in the following analytical keys, based mainly on super- 
ficial and easily distinguishable characters. 
The first key embraces the orders ; under each order is given 
akey to those genera known to occur in the region designated, 
and under each genus the species there represented. 
The geographical distribution, so far as it is known at present, 
of each of these species is indicated in the keys to species by 
the following abbreviations : — 
Arctic Ocean north of Bering Strait. 
Bering Strait, Bering Sea, Aleutian Islands, Commander Islands. 
Pacific coast of Alaska. 
Puget Sound and British Columbia. 
Central and northern California ; Monterey Bay. 
Southern California; San Pedro and San Diego. 
Gulf of California and southward to equatorial regions. 
Eastern coast of North America. 
European waters. 
A prime mark (/) indicates that the species occurs in deep water off the 
corresponding coast; the figures following indicate depth in fathoms. 
KMMN OTP RZ 
