28 BULLETIN 65, UNITED STATES NATIONAL MUSEUM. 



at fairly regular distances apart and the meshes consequently of pretty uniform 

 width, the number will be found to be about 25 (say 23-27). 



Ruedemann'^ says, in connection with the generic position of the 

 species : 



As both Spencer's drawings and our material show, these [generic] characters 

 are not retained in his second species, C suhretiformis. The latter clearly pos- 

 sesses dissepiments, which, however, are so oblique that they appear as bifurca- 

 tions [see Spencer's figure, here copied.] Dictyoncma ixtlijinorphum Gurley indi- 

 cates transition from a typical Dictyoncma with rec-tangular meshes to this 

 irregularly meshed form. The clearly closer relationship of the pre.sent species 

 to Dicti/oneina i)(>Jijinori)huin than to ('. ctjatJiifonnis has induced us to place it 

 under the former genus and to restrict Vulyi>toynii>tuis to forms which retain the 

 diagnostic characters of the genotype. 



DICTYONEMA TENELLUM Spencer. 



Plate 2, figure 4. 



Dictyoncma tcncUa Spencer, Canadian Nat., VIII, 1S7S, pp. 4."Si, 450. 

 Dictyonema tcnelliim SrENCER, Canadian Nat., X, 1882, p. 165; Trans. Acad. 



Sci. St. Louis, IV, pp. 564, 576 (not pi. 1, flg. 1.3) : Bull. Mus. Univ. 



State Missouri, I, pp. 14, 26 (not pi. 1, flg. 13). — Miller, North Amer. 



Geol. and Tal., 1889, p. 185.— Gurley, Journ. Geol., IV, 1806, pp. 06,308. 



The original description is as follows: 



Frond cyathlform in growing state, but usually circular, although occasional 

 specimens have a flabellate form in the rock. The branches are uniform, nearly 

 parallel, and radiate from the center with very few bifurcations; in width they 

 vary from one one hundred and twentieth to one-eightieth of an inch, but uni- 

 form ill the same specimen. The branches are connected at short intervals by 

 transverse dissepiments; while the margin of the frond is remarkably constant. 

 The surface is striated, and the texture has a corneous character like that of the 

 other species of this group.* 



"New York State Mus., Mem. 11, IOCS, i). 164. 



^ Here is interjiolated in the description of 1SS4, a paragrai)h which I footnote, 

 being convinced that with the exception of the statement that "between the 

 branches there are not usually spaces as great as (or greater than) their own 

 width," it has no reference to the sjiecies now under consideration. 



" In the best specimens distinct ellipsoid pits are arranged along the sides 

 of the branches, marking the positions of the calycles, these having the longer 

 diameter equal to half a millimeter and their shorter occupying two-thirds of the 

 width of the stipe. There are about twenty-four of these calycles arranged 

 longitudinally in the length of a centimeter. In specimens less perfectly pre- 

 served the bars connecting the branches are almost obliterated, and in those in 

 a better state of preservation they are placed from 2 to 3 mm. apart, while 

 between the branches there are not usually spaces as great as (or greater than) 

 their own width.'* 



Respecting the species to which he does refer, I can onlj^ say that in my expe- 

 I'ience, D. cra.smbasalc more usually than any other species, has the thecjie pre- 

 served, and that those structures in crasxihasalc could be described in about the 

 words used. But in no species could be both 0.5 mm. long, and 24 in 1 cm. — 

 R. R. Gurley. 



