No. 408.] PECTINATELLA MAGNIFICA. 967 
with many of them. Such apparently is the case, for Oka 
states that the numerous hooks of P. gelatinosa are “ minute," 
projecting beyond the annulus only 0.02 to 0.03 mm. 
In studying the hooks, I came across a number of interesting 
abnormalities that are, indeed, rather common. As already 
stated, there are typically two claws at the distal end of the 
or 
H PRT 
Fic. 9. — Abnormal forms of hooks. e with only one Ian II, type with bifid claw; 
JII, type with additional claw on one vite in first four cases below; in last case above, 
normal; ZV, type with double outgrowth ; in final case a s ekak hook is formed. 
hook. The abnormalities concern chiefly these claws. They 
may be grouped under four types (Fig. 9) : 
Type I, only one claw. 
Type II, a bifid claw. 
Type III, an additional claw — on one side. 
Type IV, a double outgrowth on one side — producing in extreme cases 
a hook with two complete double claws at its distal end. 
In addition, very rudimentary hooks, mere thread-like spines, 
are frequently found, often lying outside the typical marginal 
row. In P. gelatinosa these abnormal hooks are apparently even 
more common. Oka (90, Pl. XIX, Fig. 35) has figured some 
of them. They can for the most part be referred to the same 
