616 CAMBKIAN BRACHIOPODA. 



length of the depression; traces of a median septum occur in the dorsal valve. The grooves 

 of the main vascular canals begin in each valve at the front margin of the area and arch out- 

 ward and forward, and then, after passing the center of the valve, curve gently inward, termi- 

 nating ■ toward the front of the valve; only traces of the secondary radial canals have been 

 observed. The course of the parietal scar in each valve is probably much like that of Oholus. 

 The muscle scars, as far as known, are essentially the same as those of Oholus. In the ventral 

 valve the transmedian (i) and anterior laterals (j) occur just outside of the line of the main 

 vascular canals. The position of the outside (1) and middle (k) laterals and central (h) scars 

 is within the areas (c) on each side of the anterior termination of the median depression. In 

 the dorsal valve the centrals (h) and anterior laterals (j) are clearly defined, and the position 

 of the transmedian (i) and outside laterals (1) is indicated. The umbonal scars are small and 

 are situated in the ventral valve close to the sides of the anterior end of the furrow in the 

 area; they have not been recognized in the dorsal valve. Pedicle muscle scars unloiown. 



Type. — Trematoholus insignis Matthew. 



Ohservations. — The above description is quite urdike that given of this genus by Matthew 

 [1893a, p. 276]. It is dra-KTi up from specimens of Trematoholus insignis, lent to me, first by 

 Dr. Matthew, and later by Prof. W. A. Parks of the University of Toronto, and a fine series of 

 specimens collected by Mr. S. Ward Loper for the United States National Museum at the type 

 locality. I find that the specimen illustrated and described by Matthew [1893a, p. 276, fig. la] 

 as the interior of the ventral valve is a natural cast of the exterior of a ventral valve, preserv- 

 ing the cast of the area and the elongate depression formed by the advance of the pedicle 

 ope nin g, and that his dorsal valve (lb) is the cast of the interior of a ventral valve. The type 

 specimen of Matthew's ventral valve [1893a, p. 276, fig. la] is illustrated by Plate LXXXIV, 

 figure 5b, and the cast of it by figure 5c. The muscle scars illustrated by Matthew are slight 

 irregularities that existed on the outer surface of the shell, along the stronger lines of growth. 

 The type specimen of Matthew's dorsal valve [1893a, p. 276, fig. lb] is illustrated by Plate 

 LXXXIV, figure 5; it should be compared with the casts of the interior of the ventral valve 

 of Trematoholus Tcempanum (Matthew) as shown by Plate LXXXIII, figures Ic and Id. 



The generic relations of Trematoholus insignis Matthew and T. Jcempanum, the type of 

 the genus Protosiphon Matthew [1897a, p. 68], may be seen by comparing Plate LXXXIII, 

 figure 1, with Plate LXXXIV, figure 5c, and Plate LXXXIV, figures 5 and 5a, with Plate 

 LXXXIII, figures Id and Ij. They appear to be generically the same. The specimens of 

 Trematoholus insignis Matthew and Protosiphon pristinu^ (see Trematoholus pristinus (Matthew)) 

 came from the same stratum of rock and the same locality, and, with the correct understanding 

 of the valves of the type specimens of T. insignis, they may be closely compared, as is done 

 under the description of T. insignis. 



Trematoholus is closely related to Schizamhon. The ventral valve in both genera has an 

 oval pedicle opening in firont of the beak at the anterior end of an external groove, tapering 

 toward the beak; it is the progressive track of the pedicle aperture, and strong, arched lines 

 indicate its successive positions in diff'erent stages of growth. (See PI. LXXXIII, fig. lo, 

 which is a cast of the groove and opening in a tliick shell.) 



In Siphonotreta the pedicle opening is in front of the beak, but it does not advance with 

 the growth of the shell as in Schizamhon and Trematoholus. The surface of Schizamhon is 

 spinose while that of Trematoholus is nearly smooth. The shells of the latter are thick and 

 the former relatively thin. The muscle scars, as far as known, are essentially the same in 

 the two genera. 



It is interesting to note that, with the exception of the pedicle groove and opening, Trema- 

 toholus and Oholella are closely related. 



The species now referred to the genus Trematoholus are: T. insignis Matthew, T. pristinus 

 (Matthew), T. Icempanum (Matthew), and T. excelsis Walcott. 



T. excelsis occurs in the Lower Cambrian of eastern central California. It is one of the 

 oldest of the Cambrian brachiopods. The three species from New Brunswick are from near 

 the base of the Middle Cambrian. 



