——EE — 
NO. 3. LOOP DEVELOPMENT OF CRYPTACANTHIA—COOPER 3 
midvalve and extending to the front margin; flanks bounding sulcus 
gently convex. 
Interior.—See Internal Morphology, below. 
MEASUREMENTS IN MILLIMETERS 
Brachial Maximum 
Length length width Thickness 
FENG EG GIL Lisvsvare’'s <ierciessiersye is sateers 7.0 6.3 7.4 4.5 
Paratype 1270074. ..ccensssacs 8.9 7.8 8.9 5.1 
: T2707 Din wy sterdutaat heave 8.5 oa 8.7 4.9 
. TAZ OOTE! vor cistaausieias ore 8.0 7a 7.9 5.0 
rs WAZOOZE) sarsis ckerwisies «iste 7.5 6.7 8.2 4.7 
“4 TOTOOZE| coicc sas cae: 7.5 6.9 7.4 ‘37 
. T2ZOO7E Gwlesc os ce es 7.0 6.2 6.5 3.8 
TOTO wc zildeiny baad 6.5 5.8 6.4 3.8 
e TQTOO Ts Ssh a deo:s aiesatehn 6.0 5.5 5.9 3.2 
ol TE 7 208A Raise evoke scisie 5.6 4.8 5.3 2.6 
- T27202D) sis Ssigsinveniea-« 5.0 4.6 4.5 2.4 
i MO72OSEe oe see here cise 4.5 3.0 3.8 1.9 
£ T2a7a02d Se USE 4.0 3.5 3.6 1.6 
c T27ZO2E wy towwia aweide 3.5 3.0 3.0 2 
cs TO7T2OD saan crsicerera see 3.0 2.5 2.5 Ea 
P27 2O2E eins ckate chs sin acs 2.5 2,4 2.4 0.8 
“ T7202. atis wiseiw esa 2.0 1.7 £7 0.75 
i wepoea 8 LES 1.5 1.25 1.3 0.56 
PA72O2 ea. Va MA Sw es 1 0.87 0.04 0.44 
Types.—Holotype, U.S.N.M. No. 127066; figured paratypes, 
U.S.N.M. Nos. 127202}, k, s, u, w, z; 127203h, i, 1; 127204¢, h, 1, n, 
0, q, S, t; 127205h-j, 1, m-q, s, t; 127206k, r; 127207p; measured 
paratypes, U.S.N.M. Nos. 127202a-j; 127067a-h; unfigured para- 
types, U.S.N.M. Nos. 127202I-r, t, v, x; 127203a-g, j, k, m-z; 
1272042, b, d-g, i-k, m, p, r, u-z; 127205a-g, k, r, u-z; 127206a-j, l-q, 
S-z ; 127207a-0, q-z ; 127208a-z ; 127209. 
Discussion—The New Mexico specimens differ from Cryptacanthia 
compacta White and St. John in details of the interior as well as of 
the exterior. The Iowa species is much more robust and is much 
thicker than C. prolifica. In lateral profile the extremely deep pedicle 
valve of C. compacta has a pronounced bulge in it about a third the 
length from the anterior margin. This is a prominent feature of the 
species. A similar bulge occurs in C. prolifica but it is not so strongly 
marked as in the Iowa species. Furthermore C. prolifica is somewhat 
squarer in outline, especially when seen from the dorsal side, and has 
very distinct posterolateral shoulders. These features are not so 
prominent in the Iowa species which has much more rounded contours 
