Classijication of the Brachlopoda. — Schuchert. 151 
Order Protremata,* Beecher 1S91. 
Suborder TPUllacea,t n. suborder. 
Aphaneropegmata (part), and Productacea (part). Waagen 1883; 
lEleutherobrancliiata (part). Neumayr 1883. 
1. Family Ktjt6rginid.«. + a. faui. 
Kutorgina, Billings 1H«;1. | Schizopholis, Waageii 1885. 
:2. Family Clitambonitid^,. ? n. faui., Winchell and Schuchert. 
Orthisidii' (part), d'Orbigny 1849; Orthisiniv, Waagen 1884. 
•Clitambonites, Pander 1830. 
Pronites, Pander 1830. 
tTonambonites, l^ander 1830. 
Orthisina, d'Orbigny. 1847. 
Polvtivchia. Hall 1892. 
Protorthis, Hall 1892. 
Hemipronites, Pander 1880. 
Scenidium, Hall 1860. 
^lystropliora, Kayser 1871. 
2'. Family Pknta.mkrid.*:, McCoy 1844. 
Hypothyridic ([)art), King 1850; I'entamerida', Hall 1867 ; Caniero- 
phoriina- and Pentanierinji-, Waageii 1883; Stenoehismatina' and Con- 
-chidlina', (Khlert 1887. 
*Sonie of the oldet<t forms of this order have at maturity an incomplete deltidiuni, 
which rapidly attained its full development, so that in otlier species it covers the entire 
■deUhyriuni of the ventral valve. In the Orthid.u, the deltidiuni i8 usually absent or ru- 
-dimentary at maturity, but may be present in the nepionic and sometimes in early nealo- 
:gic stages. 
t iT/u/^a, a scoop. Having reference to the spoon-shaped plate in the ventral valve 
•("spondyliunr ■ of Hall), to the upper surface of whicli were attached the adductor, ventral 
jiedicle and divaricator muscles. 
The species of this suborder are the earliest articulate forms known. In the lowest 
primordial, there are long-hinged and rostrate forms, having usually a spondylium and 
■deltidium. These structures are regarded as of prime importance in classification, and 
species possessing then) are therefore placed at the base of the Arthkopom.\ta, and are 
considered as ancestral forms for all articulate genera. After these parts are fully devel- 
oped, the tendency, in geologic sequence, is to eliminate the spondylium, retaining the 
deltidium in the Thec.^cka, wliile in the Pentameuid.k tlie reverse has usually taken 
place. Forms wider tlian long, having a spondylium and usually a deltidium, the Cli- 
TAMBONiTn).«, became extinct with the,Devonian, while the rostrate genera, in which the 
deltidium is commonly rudimentary or absent, persist to the close of the paleozoic age. 
Those forms with a deltidium and no spondylium, tlie Thecacea, appear to be present in 
the lowest primordial, but are not characteristic until the upper third is attained, and are 
still living in Thecklinin. At tlie base of the Lower Silurian, species are developed 
w ithout either of these structures, tlie Orthid.k, passing out of existence with the pal- 
♦■ozoic. The Rhvnchoneli.ii).*; were in all probability derived from the Pentameuid^;, 
and from them developed almost siiiiultaiieously the IlELicoPEciMATA and .■Vncyi.ohua- 
<;hia. 
JThe genera referred to this family have usually been placed among the T.yoj'omata. 
K iifor(/hi(i cint/iilata, BiUingf. the tvpe of h'liforg/na, ns described and illustrated by 
Walcott (Bull. no. 3(1, l'. S. (ieol. SurV.), has more the characters of an articulate than an 
inarticulate brachiopod. This species has rudimentary articulating processes. (Jood 
examples of it show that the lateral walls of the ventral cardinal area are linear, increas 
ing in width towards the line of junction of this valve with the dorsal, and it is here that 
the rudimentary teeth are situated. In Sc/iisop/iol/s, the rudimentary cardinal walls of 
Kutorqinii are fully developed, the delthyrium is reduced to a narrow triangular fissure, 
which ' in the latter nearly occupies the entire jxisterior area. Beecher has also 
observed that A', rhigiilata has a short, perforated, deltidium in the apical portion of the 
ventral valve. 
gThis family is proposed for the long-hinged forms with spoiidylia, the majority of 
which also have a well-develojied deltidium perforated for the passage of the i)edicle. 
The PKNTAMEUiD.t; is restricted to the rostrate forms of essentially the same internal 
structure, with the deltidium usuiiily entirely or i),irtially obsolete in ndiilt specimens. 
