4/2 NEW YORK STATE MUSEUM 



LASIOGRAPTUS LapWOTth. I 873 



The genus Lasiograptus was erected by Lapworth in 1873 an d 



described as follows : 



In the adult polypary of the species of the second type, a slender spine 

 is developed from the outer margin of each theca. At a small but constant 

 distance outside the general boundary of the polypary, this spine subdivides 

 into (or gives off) numerous minute threads, which inosculate with those 

 originating in a similar manner from the spines immediately above and 

 below. These threads form a connected network or braid almost com- 

 pletely surrounding the polypary. Perfect examples are excessively rare, 

 but the specimens belonging to the group can be recognized at once, their 

 margins being apparently furnished with minute tufts of tangled hairs. 



As the type of the genus, L. costatus Lapworth ( = L . h a r k- 

 nessi Nicholson) was named. Two more British species were later made 

 known in L. margaritatus [1876] and L. retusus [1880] by the 

 same author. The former is described as having a continuous series of 

 marginal meshes completely surrounding the polypary, while the latter did 

 not exhibit any exterior meshes in the type specimens and was referred to 

 the genus on account of the form of its thecae. 



Hall described in volume 1 in Graptolithus mucronatus a 

 type with similar thecal form and marginal fibers, that was recognized by 

 Lapworth in the Scottish rocks and referred with some doubt to his genus 

 Lasiograptus in 1877. Meanwhile Hall had made his well known observa- 

 tion of subtriangular appendages of the rhabdosomes in "Grapt. w hi t- 

 f i e 1 d i " [see text fig. 458-61] and described and figured these as reproduc- 

 tive sacs [1865], a view which was generally accepted. When similar lateral 

 processes were found in D i p 1 o g r a p t u s bimucronatus, it was sug- 

 gested by Carruthers [in manuscript, see Lapworth, Ann. & Mag. Nat. Hist. 

 1880, p. 188] that this form and the very similar D . m u c r n atus should 

 be placed into a new genus under the title of Hallograptus. Lasiograptus 

 and Hallograptus were united by Lapworth \o/> c//.] with Retiograptus and 

 Glossograptus under the Lasiograptidae and Lasiograptus defined as 

 including only " those forms in which the ' reproductive sacs' appear to 

 have been protected by a continuous series of marginal meshes" and Hallo- 



