286 SYNOPTIC COLLECTION. 



areas and straight hinge line. The deltaria are formed 

 and become united into one plate, but with age they are 

 removed by accident or resorbed, so that usually the 

 delthyrium is -open. 1 In the old age stage some species 

 form a callosity in the pedicle cavity which extends across 

 the delthyrium and reaches in extreme cases nearly to the 

 cardinal margin. The median septum in the pedicle valve 

 is found in the young but seldom in the adult. 



The very young stages of some species of Spirifer have 

 a Centronella-like loop which passes through a metamor- 

 phosis. The descending branches in this genus are be- 

 tween the spiral cones (Nos. 706, 707), and the apices of 

 the latter point outward and upward (No. 707). The 

 spiral cones (No. 706, lower left hand corner, two single 

 specimens from two shells) may have a greater number 

 of volutions in the adult or the old age stage than any 

 other genus, as many as thirty-five having been counted. 



The jugum is discontinuous and is represented by two 

 short processes, one of which is seen in the right hand 

 lamella of No. 707. A faint median septum is sometimes 

 present in the brachial valve. 



Meristina is another specialized form. No. 708, M. 

 maria Hall, is a vertical section through the outer shell 

 revealing one spiral cone and cut to show the position of 

 the loop. In No. 709 these cones are seen to point out- 

 ward on each side and to consist of many whorls. 



Enough has been said to show that there is a far 

 greater degree of specialization among the Telotremata 

 than in the other three orders of Brachiopods. The arm 

 supports are extremely complex, and the devices which 

 have arisen to meet the needs of the muscular system are 

 novel and various. Unlike the Atremata there are num- 

 erous examples of old age forms in this order. 



1 I3th Ann. Rep. State Geol. N. Y., 1893, II, p. 752. 



