2 PROCEEDINGS OF THE NATIONAI^ MUSEUM vol. C(5 



high strongly incurved beak and is also characterized by long, well- 

 defined cardinal slopes. Well-developed, elevated, convex deltidial 

 plates are present. The brachial valve is also strongly incurved in 

 the apical portion. The valves are either smoothly convex (possibly 

 only in immature individuals) or have well-defined median sinuses. 

 The shell is much thicker than in most pcntameroids and is fibrous. 

 The septum of the pedicle valve is relatively very short and supports 

 a spondylium of great length. The septa of the brachial valve are 

 discrete, subparallel in relation to one another, and support crural 

 plates similar to those of (Jojichidium. 



Genotype. — HavfidiuiR insignis., new species, has been chosen as 

 the type of the genus. 



Harjjdium resembles Conchidium in the general proportions and 

 contours of its valves. The median sinus in each valve is also a 

 character that occasionally is to be found in Conchidium. It differs 

 from Conchidium., hovvever, in its nonplicated shell and in the 

 shortness of the septum in the pedicle valve. The heavy, convex, 

 elevated deltidial plates are also very different from the deltidial 

 plates of Conchidium. The spondylium is of about the size and 

 proportions to be found in Conchidium. The genus resembles Pen- 

 tamerus in that the shell is nonplicated. There its resemblance 

 ceases. The highly arched incurving apical portion of the valves, 

 the long well marked cardinal slopes of the pedicle valve, the median 

 sinuses of both valves, and the internal structures set the genus 

 clearly apart from Pcntamerus. Ilavpidiunx and Conchidium are, 

 I believe, much closer genetically than either is to Pentamerus- In 

 this connection it is of interest to note that as yet no true Pentam- 

 erus has been found in faunas of the north Pacific type. In the 

 Porcupine River region of the interior of Alaska what appears to 

 be a Pentamerus has been found. This interior region of Alaska, 

 however, lias as a rule closer affmities with the Rocky Mountain 

 Geosyncline and the interior of North America than it has with the 

 true Pacific region. The more or less complete separation of Pacific 

 and interior faunas seems to have held up to the time of the high 

 middle Devonian when there seems to have been fairly free com- 

 munication between the two faimal regions. 



KARPIDIUM INSIGNIS. new species 



Plate 1, figs. 1-G; plate 2, fig. 7 



This species reaches a fairly large size. The largest fairly perfect 

 individual in the collections gives the following measurements: 

 Length (pedicle valve), 7.5-1- cm.; maximum breadth, 6.5 cm.; maxi- 

 mum depth, 7.5d:: cm. Fragmentary material indicates that the 

 species attained a size perhaps half again as large. Smaller speci- 



