FOSSILS OF THE CLINTON GROUP. . 545 



meter one specimen showed a siphuncle .5 mm. wide. At a diameter 

 of 10 mm. another siphuncle was 1 mm. wide. 



Whether certain specimens in the marl at Huffman's Quarry, which 

 consists only of casts of the siphuncle, are" to be associated with this 

 species as an indication that also the larger forms existed there, remains 

 to be proved. One of these siphuncle casts was 2mm. broad and three 

 of the segments occupied a length of 10 mm. 



Small specimens, not exceeding 6 mm. in breath, showing all the 

 characters above described except the problematical structure of the 

 casts occasionally present in the marl specimens, and lacking the exterior 

 surface, are found at Todd's Fork in the upper ferriferous courses, and 

 seem to belong to the more typical forms of this species. 



Orthoceras inceptum, var acceleratum, var. nov. 



( Plate 37 A, Fig. 10.) 



A single specimen in the collection of Geo. Caswell, from Soldiers' 

 Home is remarkable foi the rapidity with which the distance between 

 the septa increases with growth. For this we suggest the term: variety 

 acceleratum. 



Orthoceras (Cycloceras) Nova-Car tislense, Foerste. 



( Plate 30, Fig. 25 ; P.ate 33, Fig. 1.) 



This species is rather common at Brown's Quarry. (Proceedings 

 Boston Soc. Nat. Hist., 1889.) Its exterior surface is transversely striated, 

 about 40 striae occupying a length of 20 mm. Other specimens showed 

 twelve to thirteen striae in a length of 2 mm. These much finer and 

 closer striae are interpreted as belonging to the inner shell of the species 

 Neither surface shows longitudiual striations. 



Orthoceras (Spyroceras?) spyroceroides, sp. nov. 



Associated with Orthoceras Nova-Carlislense at Brown's Quarry is 

 another form, presenting the same stout cylindrical siphuncle almost 4 mm. 

 broad, there being 8 septa in 32.5 mm. where the shell is 29 mm. broad. 

 The rate of increase and general habitus is the same as that in the preced- 

 ing species, and it would be associated with it were it not for its surface 

 ornamentation. The writer feels dubious whether all forms intermediate 

 between this and the last species will not eventually be found, but since 

 writers who have made special study of Orthoceratid^ seem to arrive at 

 conclusions that the distinctions to which we here call attention, are of 

 subgeneric if not of generic value, it seems necessary at least to place this 

 form in another species. It shows quite distinct transverse striae, 

 about 40 striae in a length of 43 mm. although that is of course likely 

 to prove a variable feature. The longitudinal striae are very fine, about 

 twelve of the stronger ones occupying a width of 8 mm., but very much 

 finer, almost hair-like striae, which require a lense to be seen, are inter- 

 calated between these. 



