30 
MUSEUM BULLETIN NO. 3. 
Diagnosis of the Genus. Shells extremely small; generally 
longer than wide; anterior margin straight or reentrant; ventral 
valve very convex, subcarinate with a narrow median groove at 
the anterior margin; dorsal valve only slightly convex at the poste- 
rior end, but concave with a deep sinus at the anterior margin 
and in this sinus there may be a small rib ; surface of both valves 
smooth. Dorsal hinge plate with a distinct cardinal process 
from which an elevated median ridge extends almost to the an- 
terior margin. The crura are slender, short, almost horizontal, 
giving off two triangular crural apophyses which converge in- 
ward and ventralward almost to the point of meeting. The 
principal lamellae extend forward to within a short distance of 
the front and are then reflected posteriorly to form the loop 
which is not angular, but uniformly curved; it rises above 
the primary lamellae until its apex is on a level with the crural 
apophyses, having been reflected a distance equal to about half 
the length of the primary lamellae. Shell structure plentifully, 
but not thickly punctate (this was demonstrated by treating 
the shell with hydrochloric acid and specimens so treated are 
studded with small needle-like elevations) Genotype Wald- 
heimia mawii Davidson. 
The matured loop of this genus is very like that of the final 
metamorphosed form as developed in Waldheimia or Magellania, 
but the resemblance is one of parallelism. In Protozeuga the 
loop develops direct and without metamorphosis in a way similar 
to that of the Devonian Centronellidae, while in Waldheimia or 
Magellania the mature loop is the final stage of a great series of 
developmental changes. This character and others given in the 
diagnosis show Protozeuga to be a primitive type of terebratulid 
whose systematic position is near the Centronellidae; but in a 
family distinct therefrom, the Protozeugidae. To this genus are 
referred Waldheimia mawii ; W.? glassii Davidson, a somewhat 
larger form whose brachial apparatus has not yet been demon- 
stated, both from the upper Wenlock of Shropshire; W. bicari- 
nata Angelin from Gotland, considered by Davidson as identi- 
cal with W. mawii; Protozeuga suloomarginata Savage from the 
Girardeau Limestone of Illinois and Missouri (Bull. Geol. Soc. 
Mo., vol. 24, p. 359, 1913); and the new species from Anticosti 
described as Protozeuga anticostiana . 
