116 THE NAUTILUS. 
been evolved since the Eocene. All of the larger forms have very 
numerous marginal tentacles on the mantle, corresponding somewhat 
to the external sculpture of the shell in position, and there is alsoa 
second inner row of “ guard tentacles” on a raised inner pallial 
fold. The marginal tentacles are accompanied by a series of well 
formed pallial eyes, very lustrous when living, and having a erys- 
talline lens. These are also arranged according to the ribs of the 
shell. In some of the deep sea forms there are but few eyes, and in 
some cases they are not pigmented. Pectens, as is well known, are 
good swimmers, although the very inequivalve typical forms are 
rather sedentary. This probably enables them to escape the attacks 
of crabs, fishes, etc., as well as boring gastropods, for itis certainly 
true that bored Pectens are rarely seen. 
The nomenclature is thoroughly sifted, and the genera and sub- 
genera characterized, 27 being recognized, of which 8 are new. 
The subdivision seems rather minute to one accustomed to the old 
order of things, but has doubtless been well considered. Of the 
genera, Pecren restricted, scarcely occurs on our coasts. AMU- 
sIuM is represented by a couple of deep sea forms, but the Oriental 
species is a well known shell. Thesubgenus Propeamusium contains 
small species such as Dall’s alaskensis. CHLAMys, type islandicus, 
is well represented, C. irradians, dislocatus, etc., belonging here to 
the subgenus diquipecten. Lissopecten is a new subgenus proposed 
for CO. hyalinus Poli, and Leptopecten another for C. monotimeris of 
California. Placopecten is proposed for P. clintonius Say, also as a 
subgenus of Chlamys. LyRoPECTEN contains L. nodosus, subnodo- 
sus, ete. PECTINELLA is a new genus for P. sigsbei Dall of the 
West Indies in deep water. CyCLOPECTEN is a new genus for P. 
pustulosus Ver. and many other small species, mostly of deep water. 
Hyalopecten, n. gen., type P. undatus Ver., contains small forms pos- 
sibly related to the fossil genus Syncyclonema. PARAMUSIUM, type 
P. Dalli Smith, is another new genus. 
Several new forms are described, with useful notes on. others, 
among which we may mention with approval the rejection of Gme- 
lin’s misleading name magellanicus for the well known New Eng- 
land species. Verrill calls it Chlamys (Placopecten) clintonius Say. 
A yery useful analytical key to the genera is given, and six well 
drawn plates illustrate important structural features and unfigured 
species. 
