Tkoi'idoleptus Fauna at Cananm)AI(;l"a I,akk, N. ^^ 129 



diductors become quite clearly defined in the ventral valve. 'I'hey are 

 large, flabelliform, and extend about half way to the front of the valve. 

 They are limited posteriorly by a pair of ridges which extend outward 

 from the bases of the teeth. Between the two diductors is a low 

 rounded septum, on each side of which is a narrow oval adductor 

 scar. Directly below the posterior ends of the teeth is a fairly deep 

 pedicle muscle scar, often divided by the septum. Posterior to this, 

 inside the beak, there is a continuation of the ventral area, of the same 

 appearance and width as the external portions of the area. It serves 

 to reinforce the umbo, which is encroached upon by the pedicle. 

 This is the striated portion of the interior taken by Hall and Clarke 

 (Pal. N. Y., Vol. VIII, pt. II, p. 302) for the attachment of the 

 pedicle muscle. 



In the brachial valve, the muscle scars are not well marked. The 

 adductors are large, flabelliform, with faint radiating ridges dividing 

 each into several parts. They extend over half way to the front of 

 the valve, and a section shows that the shell is thickened, forming a 

 platform for their attachment. 



Cardinal Process. — The cardinal process is large and prominent. 

 It extends into the delthyrium of the ventral valve, nearly filling it. 

 The main part of the process is posterior to the hinge line. It is 

 joined in front to the bases of the crura, and between them is a 

 thickening of the shell, forming a platform which slopes down to the 

 floor of the valve. On either side of this platform are the deep dental 

 sockets which are crenulated on their posterior walls. In a large 

 specimen the cardinal process is about 2.5 mm. wide, The posterior 

 face is smooth and rounded, and the lower third is covered by a strong 

 chilidium which also bounds the posterior ends of the dental sockets. 

 The smallest specimen on which the chilidium could be seen was 

 3.5 X 2 mm. and the chilidium was .06 mm. in width. On a specimen 

 6x6 mm. it was .25 mm. wide and on an adult 1.5 mm. wide. 



The posterior wall of the cardinal process has, near the top, a 

 narrow rounded sinus and, in the bottom of this sinus, the shell is 

 continued forward and downward until it unites with the platform of 

 the process, thus forming a shelly loop. On either side of this loop 

 is a deep conical hole which extends nearly to the apex of the shell 

 and probably represents the place of attachment of the diductor 

 muscles. Directly in front of the loop is a groove in the platform 

 leading to a minute anal tube which runs through along the middle 



