552 THE AMERICAN MIDLAND NATURALIST 



ervation) the classification of these fossil plants becomes more truly phyletic. 

 Lack of diagnostic information due to vagaries of preservation will probably 

 always make it necessary to recognize non-biological distinctions to some extent 

 in scientific classification. Lepidocarpon, however, appears to be an example 

 where these differences can be relegated to less than generic importance. 



Lepidocarpon Scott (1900) 



(Revised diagnosis) 

 A genus of ligulale lycopsid plants characterized by, 



(1) Strobilar habit of fructification; 



(2) Sporophylls attached to cone axis as in Lepidostrobus ; 



(3) Sporophylls shed entire by disintegration of the cone axis ; 



(4) Seeds provided with a distinct integumentary organ; 



(5) Integument, attached lateral to sporangium along pedicel, invests the sporangium 



closely and its trvo edges project ventrally above the seed body as a micropylar 

 crest ; 



(6) Slit between the two membranes of the crest corresponding morphologically to a 



micro pyle ; 



(7) M egasporangium large, indehiscent (fertile spore not shed), attached for the 



greater part of its length to the ventral midline of the pedicel; 



(8) Outer wall of sporangium of prismatic or columnar cells, similar in structure to 



the sporangium wall of free-sporing lycopods; 



(9) Intrasporangial tissue more persistent than in most free-sporing lycopsids; 



(10) Seed megaspore relatively enormous (for lycopsids), spore coat with more or less 



fibrous texture and trilete apparatus at its proximal end (usually turned toward 

 the anterior or distal end of the seed); 



(11) Maturation of only one seed megaspore per sporophyll, derived from a single 



tetrad; abortive megaspores also evident. 



English Species of Lepidocarpon 



The cone of the genotype species, Lepidocarpon lomaxi Scott, is medium 

 sized (20-30 mm. diameter), of compact structure with sporophyll laminae 

 long and strongly reflexed upwards. Toward the tip of each lamina the blade 

 seems to have been membranous and impersistent but near the seed it was 

 rather fleshy and is commonly well preserved. Mature seeds are fully integu- 

 mented but the integument is frequently incomplete on immature specimens, 

 and in this condition it is represented by fleshy cushions along both sides of 

 the pedicel. The integument is presumed to have been formed last, late in 

 ontogeny. A simple layer of columnar or prismatic cells, very similar to the 

 prismatic layer of Lepidostrobus, covers the sporangium. Radial length of fruit 

 is 8-14 mm., - — tangential height through seed body 5-11 mm., — width at 

 distal end of seed body 5-12 mm. This species occurs in the English "Lower 

 Coal Measures." It has been reported in most coal seams of this age that have 

 provided coal balls, and thus it must be considered a rather widespread and 

 characteristic element of the upper Lanarkian flora. 



Scott also described a second much older species, L. wildianum, from the 

 Calciferous Sandstone at Pettycur that is somewhat smaller than L. lomaxi, 

 but otherwise not readily distinguishable. The seed megaspore shows an "irreg- 

 ular reticulation" (Scott, 1901, p. 315) which in all likelihood is similar to the 

 fibrous network composing the Cystosporites membrane. L. wildianum is doubt- 

 less a distinct species, and future studies will probably make known biological 



