366 



CAMBRIAN BRACHIOPODA. 



number of widely separated radial lines. As regards the substance of the shell, it must be remarked that it is exactly 

 the same as in the genus Siphonotreta, i. e., calcareous-horny, and of a brown color. Under the microscope, enlarged 

 six to eight times, the valves show a fine but distinct puncturing, invisible to the unaided eye. 



As regards the dimensions of the shell, the largest examples have a length of 14, a breadth of 19, and a thickness of 

 16 mm., while the height of the ventral valve is 10 mm. 



Hall and Clarke [1892c, p. 96] compare this genus with Kutorgina on account of the general 

 form and surface characters, and call attention to the presence of an areal ridge similar to that 

 of " Iphidea" = Micro7nitra. Tlie authors were under the impression that an apical foramen 

 existed in Micromitra and probably in Volhorthia and that the areal ridge was the "ecurved" 

 foramen scar. I do not find a foramen in Micromitra, and none has been seen in Volhorthia. 

 The areal ridge appears to be the arched pseudodeltidium, both in Micromitra [PI. Ill, fig. 3b] 

 and Volhorthia [PI. I, fig. 6e]. 



The previously published illustrations of Volhorthia recurva do not show any opening 

 between the posterior margins of the valves, but that there was an opening for the passage of the 

 pedicle is shown in figures 33A and 33A'. 



The absence of defined muscle scars and vascular markings is a characteristic of this genus. 



The generic name was given in honor of Dr. A. von Volborth. 



Type. — Acrotreta recurva Kutorga. 



^, VOLBOETHIA RECURVA (Kutorga). 



Text figures 33A-B; Plate I, figures 6, 6a-e. 

 Acrotreta recurva Kutorga, 1848, Verhandl. Russ.-kais. min. Gesell. St. Petersburg for 1847, No. 12, pp. 277-278, PI. VII, 

 figs. 9a and 9d. (Characterized and discussed in German as a new species. The description of PI. VII gives 

 the name of the species as "Acrotreta incurva." The only figm-es accompanying the reference are those men- 

 tioned, 9a and 9d.) 



FiGtniE 33. — Volhorthia recurva (Kutorga). A, Posterior view of specimen figured by von Moller, 1874, PI. Vn, figs. 1-6. 



A', Enlargement of same to show pedicle opening, light from the right. B, Posterior view of an associated ventral 



valve showing crenulation of the striae on the false area. 



The specimens represented are from Locality 336g, limestone in the vicinity of Zarskoe Selo, Russia. The 

 specimens are now in the museum at Reval, but a cast of the type specimen represented in figures 33A-A' is in the 

 collections of the U. S. National Museum, Cat. No. 5S29S. 



Volhorthia recurva (Kutorga), von Moller, 1874, Neues Jahrb. fiir Mineralogie, pp. 449-452, PI. VII, figs. 1-6. (The 

 description and discussion of the species is included in that of the genus, which is in German and which is trans- 

 lated on pp. 355-356. Pigs. 1-6 are copied in this monograph, PL I, figs. 6, 6a-e, respectively. The specimen 

 represented by figs. 6, 6a-e of von Moller's paper is redrawn in this monograph, figs. 33A-A'.) 



Volhorthia recurva (Kutorga), Hall and Clarke, 1892, Eleventh Ann. Rept. State Geologist New York for 1891, figs. 

 261 and 262, p. 249. (No text reference. Figs. 261 and 262 are copied from von Moller 1874, PI. VII, figs. 2 

 and 6, respectively.) 



Volhorthia recurva (Kutorga), Hall and Clarke, 1892, Forty-fifth Ann. Rept. New York State Mus. for 1891, figs. 261 

 and 262, p. 565. (Copy of preceding reference.) 



Volhorthia recurva (Kutorga), Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 95-96, 

 figs. 52 and 53. (The description of the species is included in that of the genus, which is translated, essentially 

 as on pp. 355-356 of this monograph, from von Moller, 1874; pp. 449-451. Figs. 52 and 53 are copied from 

 von Moller, 1874, PL VII, figs. 2 and 6, respectively.) 



The generic description includes the important characters of this, the only known species. 



Formation and locality. — Ordovician: (336g [Kutorga, 184S, p. 27S]) Limestone in the vicinity of Zarskoe Selo; 

 and (337j [Fr. Schmidt, personal communication, 1908]) zone Blllnr or BIII/3, characterized by Asaphus raniceps, a 

 little above the zone with Asaphus expansus, at Obuchow (Obookhov), on Wolchow River; both in the Government 

 of St. Petersburg, Russia. 



