626 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
smooth. Sulcus occupied by 2 or 3 costae, and 3 or 4 occur on the brachial fold. 
The flanks are marked by 2 or 3 costae. 
Pedicle valve in lateral profile fairly strongly convex in the posterior half but 
somewhat flattened in the anterior portion. Anterior profile moderately convex 
with a slight depression at the middle in some specimens. Sulcus short, wide, 
and shallow, producing a short, broadly rounded tongue. Areas bounding sulcus 
moderately convex, while the flanks of the shell are moderately convex and with 
steep lateral slopes. 
Brachial valve strongly convex in lateral profile with the maximum convexity 
slightly posterior to the middle. Anterior profile moderately convex. Fold low 
and not prominent, defined at the anterior only. Body of shell slightly swollen 
and with steep lateral slopes. 
Measurements in mm.— 
Brachial 
Length length Width Thickness 
Holbtypervn.insun aloes «Levetal oh 4.8 4.3 5.0 2.9 
Paratype «(GET 2R2b ici bes aciabisehee 4.8 4.3 5.4 22 
* GE D620).. wietact tlie deat 4.5 3.9 4.2 2.8 
Types.—Holotype: 111282a; unfigured paratypes: 111282b,c. 
Horizon and locality—Mingan formation (zone A5) in Quebec, Canada: 
Mingan (or Bald Island), Mingan Islands, St. Lawrence River. 
Discussion.—These little shells combine some of the exterior features of 
Ancistrorhyncha and Camerella. The costation is like that of Camerella in its 
shortness and strength. Most other species of Ancistrorhyncha are completely 
costate and the costae are generally finer and more numerous. The folding of 
this little species is, nevertheless, like that of Ancistrorhyncha. The determining 
factor for placing the species in Ancistrorhyncha is its internal structure—or in 
this case, lack of internal structure. The shells are filled with crystalline calcite, 
a fact that makes determination of the interior details very difficult. Twenhofel 
(Twenhofel and Whiting, 1938, p. 54) assigned specimens from the same place 
and horizon to Rhynchocamara varians and regarded them as the young of that 
species. Twenhofel stated that the specimens had been entirely replaced by 
crystalline calcite. This is not true; the shells have been filled but not replaced 
by the mineral because the fibrous nature of the shell is still retained. 
In order to study these specimens, they were immersed in water and examined 
in a strong light. By this method a certain translucency of the outer shell was 
obtained. If these specimens belonged to the genus Rhynchocamara, the strong 
median septum of both valves would have been visible. The brachial valve re- 
vealed no trace of septa which would have been clearly visible in the few shells 
filled by opaque calcite. The pedicle valves showed short dental plates. This 
combination of characters in the pedicle valve and lack of septa in the brachial 
valve in connection with the Ancistrorhyncha-like external expression led to the 
placing of the species in that genus. 
This species differs from all those herein described by its naked umbos, strong 
costae, and general resemblance to Camerella. 
