C. E. Beecher — Development of the Brachiojpoda. 355 



Protremata. 

 (7rpGD, early, and rpr}jxa y perforation.) 



Plate xvii, figures 13-21. 



Protegulum of the brachial valve as in the Atremata. In 

 the pedicle valve, it has become modified through acceleration 

 to an elliptical or circular form with arcuate hin^e. Pedicle 

 enclosed in early nepionic stages by shell growth ; posterior 

 covering (pseudo-deltidium) retained at maturity, or resorbed 

 or abraded in nealogic stages, so that the pedicle protrudes 

 between the two valves. The stages of growth, in general, 

 represent (1) a paterina stage, with straight hinge line and 

 pedicle opening shared by both valves ; (2) a discinoid stage, 

 without straight hinge, pedicle enclosed by concentric peri- 

 pheral growth of pedicle valve ; and (3) a straight hinged con- 

 dition, with pedicle opening either retained or merged into 

 fissure of hinge area. Valves articulate. 



Including the genera : — 



Amphigenia. 

 Aulosteges. 

 Bactryniurn. 

 Bilobites. 



Camarella (group). 

 Camarophoria. 

 ^Chonetes. 

 Clitambonites. 

 Conchidium. 

 Davidsonella. 

 Davidsonia. 

 Daviesiella. 

 Derbya. 

 Enteletes. 

 Eudesella. 

 Hemipronites. 

 Hipparionyx. 



*Lacazella. 

 *Leptsena. 



Leptsenisca. 



Lyttonia. 



Meekella. 



Mimulus. 



Oldhamina. 

 *Orthis (group). 



Orthisina. 

 *Orthotetes. 



Pentamerella. 



Platystrophia. 

 *Plectambonites. 



Porambonites ? 



Proboscidella. 

 *Productella. 



Productus. 

 *Rhipidomella. 



Schizophoria. 



Sieberella. 



Streptis. 

 *Streptorhynchus. 



Stricklandinia. 



Strophalosia. 

 *Stropheodonta. 

 *Strophomena. 

 *Strophonella. 



Thecidella. 

 *Thecidium. 



Thecidopsis. 



Tripled a. 

 *Tropidoleptus. 



Telotremata y 



(riAo?, last, and rprfjj.a y perforation.) 



Plate xvii, figures 22-28. 



Protegulum as in Atremata. Pedicle opening shared by 

 both valves in nepionic stages, usually confined to one valve 

 in later stages, and becoming more or less limited by two 

 deltidial plates in ephebolic stages. Arms supported by cal- 

 careous crura, spirals, or loops. Yalves articulate. 



Including the genera : — 



