TESTICARDINES : INTERNAL CHARACTERS 



501 



example, we notice first in the dorsal valve the " crura " (rr), 

 IVom which arise the two "descending l)ranclies" which rnn 

 forwards and then are bent hack to fonn tlic "ascending 

 branches" which are united by the " transverse band." In some 

 genera the "ascending branches" maybe reduced to mere points, 

 and the "transverse band" become a median vertical phite ; the 

 " ci'ui'a," too, may be fused so as to form a "crural band"; and 

 the "descending branches" may be connected by a cross band — 

 the "jugal band." In String ocephahis (Fig. 326, /, s.p) the loop 

 is furnished on its inner edge with radiating processes; and 

 in Argioj^e the loop is simple, not reflected, and fused with 

 marginal septa ; while in the Thecidiidae it is more or less fused 

 with the shell itself, and with the mass of calcareous spicules 

 secreted by the mantle. 



The "spiral-cone type" of Ijrachial apparatus is found in the 

 Spiriferidac, Atryindac, and Konincldnidae , and consists of two 

 spirally-enrolled calcified lamellae, forming two cones with their 

 apices directed laterally {Spirifera, Fig. 330), or towards the 

 interior of the dorsal valve {Atryp)a, Fig. 3 .'5 2), or towards 

 each other (Glassia) ; or forming two flat spirals in the same 

 plane {Koninckinidae). A " jugal band " is generally present, but 

 varies much in position, 



and in some genera lias ,^d^^^^^^ 



complicated posterior pro- 

 cesses. 



The lUiyiirli oncllidae 

 liave no loop or spiral 

 cones, but merely a pair 

 of short " crura." 



The ])rinci])al nioiliti- 

 cations in the attacliments 

 of the muscles in the 



Ti'stlvdrdinrs are illustrated l»y Productus gigfi?iiriis (Fig. 333), 

 Lcptaena rhonihoidalis (Fig. 334), and Waldhcimiir Jlavescens 

 (Fig. 329). 



In I'rddi'ctiis (Fig. 333) we see in the ventral valve a jiaii- of 

 dendritic occlusor, often called adductor, impressions and a pair 

 of large fiabellate divaricator impressions. In the dorsal valve the 

 large " cardinal process " served for the attachment of the divari- 

 cator, and a low me(Han s('i)tum se])arated tlie deiKh'itic occlusoi- 



Fig. 330. — Spirifera drudn. (Carboniferous Lime- 

 stone. ) Showing brachial spires. 



