BRACHIOPODA. 337 



Terminology.] 



v., vascular sinuses. 



add., adductor muscle scars. 



did., diductor muscle scars. 



adj., adjuster muscle scars. When the pedicle muscular scar is present, it appears 

 in the apex of the rostral cavity, posterior to the other scars, and is indi- 

 cated by transverse striag. 



m. sep. 



FIG. 23. a, interior view of the ventral valve of Clitambonites diversa Shaler; 6, dorsal view of 

 Zygospira modesta (Say) Hall, from which the greater portion of the dorsal valve 

 has been removed to show the calcified brachial supports. 



spond., spondylium, a plate formed by the junction of the dental plates, to the 

 upper surface of which were attached the adductor, diductor, and adjuster 

 muscles. This plate is also present in the Pentameridce. 



m. sep., median septum supporting the spondylium. 



d. p., deltidial plates. See deltidium. 



spire, the spiral cones or calcified brachial supports. The spires may be directed 

 toward the center of the dorsal valve or with their apices toward the 

 lateral margins. The lamellae are usually single, but a number of genera 

 have two bands in each spiral cone. The brachial supports also may be 

 short or long hooks or crura to which the fleshy arms are attached, as in 

 Rhynchonella, or they may form a more or less complicated "loop," as in 

 the terebratuloids. For an illustration of a loop, see the species of 

 Hallina of this report. 



c. b., connecting band or loop; it is variously disposed, and of a great variety of 

 forms growing out from each spiral cone, and may or may not join medi- 

 ally. In Atrypa and Spirifer, the band is represented by two prongs. 



Protegulum, Beecher. The initial shell of brachiopods. It is smooth and of micro- 

 scopic size, in outline semicircular or semielliptical, with a straight 

 or arcuate hinge line and without a hinge area. Homologous to the 

 "protoconch" of Owen in cephalopods, and to the "prodissoconch" of 



Jackson in lamellibranchs. 

 -22 



