I5r) 
The American Geologist. 
March, 1893 
Suborder HeliCOpegrnata.* Waagen 1K8:5. 
Sl)irirer!K'(>u, Waa^eii 1883. 
Family ATRVi'ii).i':,t Dull 1877. 
Siil)t'ainily Zvo(»si'Jrin.i;, Waagen 1888. 
Aiiazygidii' (])art), Davidson J8S4. 
iZygospira, Hall 1862. 
Stenocisma, Hall 1847 (not 
Conrad 1839; Hall 1867). 
Anazyga, Davidson 1882. 
Orthononuca, Hall 1858. 
Glassia, Davidson 1882. 
(\elospira, Hall 1863. 
Leptoc.'lia, Hall 1857 (not 
1859). 
Anoplotlieca, Sandberger 1856 
Subfamil}' Atrypin>^, Waagen 188;}. 
Atrypa, Dalman 1828. 
Cleiothyris, Phillips 1841 (not 
King 1850). 
Spirigerina, d'Orbigny 1847. 
(rriinewaldtia, Tsehernyschew 
1885. 
? Karpinskya, Tsch. 1885. 
Family Spiriferid^, + King 1846 (emend Davidson). 
Martiniin<ie and Keticulariin;e, Waagen 1883; 8piriferinida% David- 
son 1884. 
1. Subfamily SaEssiiN>«, Waagen 1883. 
•Cyrtina, Davidson 1858. 
Delthyris, Dalman 1828. 
„Spiriferina, d'Orbigny 1847 
Suessia, Deslongchamps 1854. 
Mentzelia, Quenstedt 1871. 
1'. Subfamih- Unoitin.b, Waagen 1883. 
Uncites, Defrance 1825. 
2. Subfamily Trigonotretin.b, n. subfam. 
Delthyrinif (part), Waagen 1883. 
Cyrtia, Dalman 1828. 
Syringotbyris, Winchell 1863. 
Spirifer, Meek and H. 1864. 
Martinia, McOoy 184-4. 
Spirifer, Sowerby 1815. 
Choristites, Fischer de AVald. 
1825. 
Trigonotreta, Xoenig 1825 ; 
Meek and Hayden 1864. 
*The IIelicopkgmata are distinguished in having two calcareous, simple or double, 
•spirally enrolled, brachial supports, which may or may not be attached to each other by a 
variously constructed band or "loop."' The direction of the spirals, their connection 
with the hinge plate and the nature of the loop are considered of prime importance in 
classifying the genera of this suborder. External characters are not always even of 
generic value. 
tin this family the apices of the brachiaare medially or dorsally directed. The loop 
in the Ztoospirin^ is a simple connecting band, which in adult Atrtpin^ is disunited, 
having free ends. In the Atutpidve and SrrKiFEniD.E, the primary lamellfe are straight 
from their attachment to the crural plate to near the anterior margin, and do not recurve 
near their point of origin, as in the NucleospiriDxE and Athtiud.e. 
JThe Spikiferip^e are usually much elongated along the hinge line, have postero- 
daterally directed brachia joined by a V-shaped loop in the Suessiin.e and Uncitin.<b, 
while in the Triuonotretin.* the loop is obsolescent and consists of two prongs ter- 
iminating freely, one attached to each primary lamella. 
