DICRANOCJRAPTUS. 



179 



Mr. William Swanston, of Belfast, and were presented by him to the Sedgwick 

 Museum ; other good ones are in the collections of Lapworth and the Authors. 



Dicranograptus furcatus, Hall, var. minimus, Lapworth. Plate XXV, figs. ia—c. 



1876. Dicranograptus ziczac, var. miniums, Lapworth, Cat. West. Scott. Foss., pi. iii, fig. 77a. 



1877. Dicranograptus ziczac, var. minimus, Lapworth, Grapt. Co. Down, Proc. Belfast Nat. Field 

 Club, p. 141, pi. vi, fig. 42 6. 



Fig. 114. — Dicranograptus j 

 catus, var. minimus, Lapw. 



In addition to Dicranograptus ziczac there occurs in the Glenkiln Shales a 

 nearly allied form, to which Lapworth gave the distinctive varietal name of 

 minimus. This form, however, is more closely allied to 

 Dicranog. furcatus (Hall), and should, therefore, be re- 

 garded as a variety of that species rather than of 

 Dicranog. ziczac. In this variety the uniserial stipes 

 never exceed 1*5 cm. in length, and form a single gentle 

 curve. The biserial portion resembles that of D. ziczac. 

 All the thecse, not only of the biserial portion, but also 

 of the uniserial stipes, are provided with mesial spines. 



Affinities. — Var. minimus may be distinguished from 

 all other British Dicranograpti by its peculiar shape. 

 It is very similar to Hall's D. furcatus, but differs from 

 it in having a longer biserial portion and less closely set 

 thecas. The stipes of var. minimus also have never 

 been observed to meet, whereas in D. furcatus they 

 typically cross. 

 V X*k Horizon and Localities. — Glenkiln Shales. 



(} $J^~ 8. Scotland : Dobb's Linn ; Glenkiln Burn ; Belcraig 



Y Burn, etc. Ireland : Coalpit Bay; Ballygrot. N. Wales : 



Tiddyndicwm. 



Associates. — Var. minimus is a fairly abundant form 



in some of the Scotch localities. It occurs associated 



with Dlcellog. sextans, Dicellog.patulosus, Nemag. gracilis, 



best specimens are in Lapworth's 



Distal thecai showing mesial 

 spines. Enlargement of part 

 of PI. XXV, fig. 4 c. 



Figs. 115 a and b. — Dicranograp 

 tus furcatus, Hall. 



«. Specimen (nat. 

 Hall's typical 

 Norman's Kill 

 Lapworth. 



h. Distal thecae. ( 



I 



size) from 

 locality in 

 Beds. Coll. 



5.) 



Diplog. Whitfieldi, and other forms. The 

 collection and that of the Sedgwick Museum. 



