BRACHIOPODA. 361 



chtzambon(?) dodgii.1 



said to have a short, obtuse beak at the cardinal margin, and judging from the illus- 

 tration, it seems that little growth took place posterior to the protegulum, or initial 

 shell. While no mention is made in S. typicalis and 6'. ? fissus var. canadensis Ami, 

 of shell growth posterior to the protegulum, yet undoubtedly this feature will be 

 found when looked for in specimens preserving these parts. 



The line of development was probably as follows : From Paterina to a form 

 having an open pedicle notch at the posterior end as in Schizocrania and Trematis, 

 next to one where this notch is closed, leaving a more or less circular excentric 

 pedicle opening, as in Acrothele or Acrotreta; thence to Schizctmbon. 



SCHIZAMBON(?) DODGII, n. sp. 



PLATE XXX, FIGS. 5-7. 



Shell broadly oval, or nearly circular in outline. Dorsal valve evenly convex 

 laterally and anteriorly; deeper than the ventral valve; point of greatest elevation 

 about mid-length; centrally it has a shallow, concave, narrow sinus, which has its 

 origin at the beak, thence slowly expanding in width, and traversing the entire 

 length of the valve. Surface with numerous, concentric, variously terminating 

 growth lines. Near the beak these lines indicate a Potfm'wa-shaped nepionic stage. 

 They are very delicate, the shell appearing smooth and shining, and gradually 

 assume the contour of the mature outline of the valve, becoming stronger and 

 stronger as full development is attained. Every second, third, or fourth line prom- 

 inent, strongly imbricating, wavy along the edges, and terminating in long, slender, 

 hollow(?), radiating spines. The intermediate concentric lines between the spinif- 

 erous ones are sharply elevated and finely crenulated. The spines begin to develop 

 at a very early age, are remote, but become more and more crowded toward the 

 anterior margin, where there are about sixteen in 3 mm., with an average length 

 of 2 mm. 



Ventral valve somewhat larger than the dorsal; curvature along the center not 

 very marked, with the lateral slopes broadly convex7 Beak marginal, slightly pro- 

 duced, elevated, with a small, false cardinal area beneath it. Pedicle furrow origi- 

 nating at the beak, narrowly triangular, 4 mm. in length, becoming deeply concave, 

 with an opening into the interior of the shell, probably at its inner end. The 

 nature of this opening and the interior characters of both valves are unknown. 

 At the apex, the concentric lines are first Paterina-shaped; then growth obtains 

 all around the initial shell, being more rapid anteriorly than posteriorly. It is 

 during this second stage that the false cardinal area is formed, and the position of 

 the pedicle opening changed. After the initial shell, the first few lines of growth 



