Raymond : Brachiopoda and Ostracoda of the Chazy. 251 



convex, with beaks elevated above the hinge line, and tlu- diillnriuin 

 open. Xo fold, sinus, or plications are developed. 



W lun the shell is about i mm. long it assumes a sul)lrianj;;ular shape, 

 the greatest width being toward the front of the shell. The brachial 

 beak becomes closely appressed to the hinge, and the pedicle beak 

 extends slightly behind it, the pedicle passage remaining open. This 

 form is retained until a length of from 1.5 mm. to 2 mm. is attained, 

 when a fold is developed on the front of the brachial valve, and a sinus 

 in the pedicle valve. This will be referred to as stage i. A little 

 later, when about 3 to 3.5 mm. long, a plication is introduced in the 

 middle of the sinus, thus dividing the fold into two parts or plications. 

 This is stage 2. The next step, at 4 to 4.5 mm. is the introduction 

 of a fold in the sinus between the two plications just formed on the 

 brachial vahe. This makes three plications on the brachial valve, 

 two in the sinus of the pedicle valve, and one on each side of the sinus, 

 a total of four on the pedicle valve. This is stage 3. Next, two pli- 

 cations are introduced on the sides of the brachial valve outside the 

 fold, and a corresponding pair on the pedicle valve. This is stage 4. 

 In the fifth and last stage illustrated by these specimens, another 

 plication is introduced in the sinus of the pedicle valve, making three 

 plications in the sinus, four on the fold, one on each side of the fold, 

 and two on each side of the sinus. 



The origin of the many varieties, which at first sight might appear 

 to be different species, is that development has been arrested in certain 

 individuals at each of the stages mentioned above, and the shell has 

 grown to adult size without going through the succeeding stages, or 

 else has skipped certain stages. Thus there is a specimen from 

 Cystid Point, \'alcour Island, 7.5 mm. long and 6.5 mm. wide, which 

 has only the fold and sinus, without plications (Plate XXXVI, 

 fig. 28). The general form of this specimen is somewhat like that 

 of Camarella longirostris, but the beak of the pedicle valve is incurved, 

 not extended, and the brachial valve is subtriangular instead of subcir- 

 cular. This specimen is an adult the development of which was arrested 

 at stage i. Another specimen, 8.5 mm. long and 8 mm. wide, has one 

 plication in the sinus and two on the fold. The development of this 

 individual was arrested at stage 2. The specimen is from the quarry 

 at Kings Bay, Cooperville, New York (Plate XXXVI, fig. 24). A 

 majority of the individuals have their development arrested at stage 3^ 

 when there are three plications on the fold and two in the sinus. Numer- 



