368 CAMBRIAN BRACHIOPODA. 



this species, and in only three specimens have I found what might be considered to be a perfora- 

 tion at the apex of the shell. In one of these it was clearly a circular fracture of the shell, and 

 in the other two the apex had been pushed in so as to form a small circular depression with sharp 

 edges. Several interiors of the shell also fail to show any indication of an opening through the 

 shell; the specimen illustrated by Pander [1861, PI. II, fig. 2b] and the enlargement (g) are very 

 much like the specimen with the minute circular opening caused by fracture. There are several 

 other specimens in which there is a slight depression just in advance of the beak, which indicates 

 that the shell was very thin and slightly flexible at this point. I would not venture to suggest 

 that this was an imperfect ventral valve were it not for the fact that I have such an abundant 

 supply of material which is clearly to be referred to the form described by Pander. I would 

 further state that it frequently occurs that the apex of the shell is slightly raised above 

 the surface so as to form a minute node and that when the apex is pushed in the edge of the 

 depression follows a concentric line of growth. 



If we consider that Helmersenia is not a perforate shell, it then falls in with Obolus except 

 that the area of the ventral valve is imlike that of Oholus and it has a spinose outer surface. 

 The area, as illustrated by Pander [PI. LXIII, fig. 7d], is of the MickiDitzia monilifera type 

 (PI. VI, fig. !")• The shells of Helmersenia are delicate and much more like those of Mickwitzia 

 than Oholus. The outer surface of MicJcivitzia is not known to be spinose, but if we compare 

 the surface shown by figures In and 2 (PL VI) with figures 7, 7a-b (PI. LXIII) of Helmerseniawe 

 gain an mpression of their great similarity. On account of the character of the area of the 

 ventral valve, the appearance of the shell, and its surface, Helmersenia is placed within the 

 Paterinidse. 



The generic name was given in honor of Gregoire de Helmersen. 



Helmersenia ladogensis (Jeremejew). 

 '^ Plate LXIII, firures 7, 7a-f. 



Siphonotreta ladogensis Jeremejew, 1856, Verhandl. Russ.-kais. min. Gesell. St. Petersburg for 1855-6, No. 2, pp. 73 

 and 80, figs. 5a-c, p. 73. (Described in German on p. 80, as a new species.) 



Diseina huchii Eichwald (in part) [not (de Verneuil)], 1860, Lethsea rossica, ancienne p^riode, vol. 1, sec. 2, p. 914: 

 (Includes Siphonotreta ladogensis with Diseina huchii.) 



Helmersenia Pander, 1861, Bull. Acad. imp. sci. St.-Petersbourg, vol. 3, columns 48-49, PI. II, figs. 2a-g. (Described 

 and discussed in German. Figs. 2d and 21" are copied in this monograph, PI. LXIII, figs. 7d and 7c, 

 respectively.) 



Helmersenia jeremejewi Dall, 1877, Bull. U. S. Nat. Mus. No. 8, p. 31. (See the text below for discussion of this 

 reference.) 



Keyserlingia panderi Karpinsky, 1887 (April), Bull. Acad. imp. sci. St.-Petersbourg, vol. 31, p. 476, footnote. (Dis- 

 cussed in German; see below.) 



Helmersenia jeremejewi Dall, Oehlert, 1887 (June), Manuel de conchyliologie, by Fischer, p. 1264. (Mentioned in 

 French as type of genus; see below.) 



Helmersenia sp.? Pander, Hall and Clarke, 1892, Eleventh Ann. Rept. State Geologist New York for 1891, p. 254, 

 PI. IV, figs. 6 and 7. (Mentioned in the text, which is a description of the genus. Figs. 6 and 7 are copied from 

 Pander, 1861, PI. II, figs. 2d and 2b, respectively.) 



Helmersenia sp.? Pander, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, p. 119, PI. IV, 

 figs. 4 and 5. (Mentioned. Figs. 4 and 5 are copied from Hall and Clarke, 1892a, PL IV, figs. 6 and 7, respec- 

 tively.) 



The specific description of this species has been included in the generic description. 



Pander [1861, p. 48] gave no specific name to the form which he described as Helmersenia, 

 but he refers to Siphonotreta ladogensis Jeremejew in such a manner as to indicate that he coii- 

 sidered that species as the type. 



In 1877 Dall published a list of the names applied to the subdivisions of the Brachiopoda, 

 and [1877, p. 31] designated the type species as Helmersenia jeremejeivi, ascribing the species to 

 Pander and referring to page 47 of Pander's paper. Pander [1861, p. 48] places the words 

 " Si2)lionotreta Jereiaejew" alter Helmersenia, refers to the place of publication of Siphonotreta? 

 ladogensis Jeremejew, and discusses the generic relations of the specimens before him with 

 Siphonotreta ladogensis. It is thus evident that Pander did not name the species H. jeremejewi. 



