582 



TRANS. SI . LOUIS ACAD. SCIENC] 



rudimentary denticles appearing also on the opposite side of the 

 branch as well as on that marked with the regular spine-like pro- 

 jections, of which there are six or seven in the length of a centi- 

 metre of the stipe, which is characterized by obscure indications 

 of a solid central axis. The branches average a millimetre in 

 breadth, and the spines are sometimes a millimetre long, which 

 in some places extend into the material of the stipe to its centre. 

 The flattened frond is usually four or five centimetres high and 

 about four wide, and consist of fifteen or twenty branches at half 

 its height, which are somewhat more numerous at the summit 

 owing to occasional bifurcations. The whole frond originates 

 from a common radicle. 



The best preserved graptolites that are found at Hamilton 

 occur on the shaly surface of the limestone, but this species is 

 only found in the highly crystalline rock, and consequently, al- 

 though the general form of frond is well-preserved and very 

 beautiful, the detailed structure is not shown as well as in the 

 forms that are found in the more perishable shaly rocks. 



Formation and Locality. — This species is found in the dolomitic 

 limestones of the Niagara formation at Hamilton, Ont., and was 

 first discovered by Col. C. C. Grant, after whom it is named. 



ACANTHOGRAPTUS PULCHER, nOV. Sp. 

 Plate 4. Fig. 6. 



This frond is broadly flabellate, but was possibly cyathiform 

 in its growing state. Very numerous branches (with few princi- 

 pal subdivisions) arise from a common radicle and extend in an 

 entirely free manner to the even, and more or less circular, mar- 

 gin of the frond. Along both sides of the branches many short 

 rudimentary branchlets arise. Besides these there are numerous 

 spine-like processes, which possibly indicate the position of the 

 cellules. The texture is corneous, with the surface striated, and 

 in some places, where removed, there are indications of a lateral 

 solid axis. From the centre of the radicle the branches extend a 

 distance of about two and a half millimeters to the margin of the 

 ground, or the diameter is about five millimetres. The branches 

 are half a millimetre thick. The rudimentary branchlets, irregu- 

 larly situated, are seldom more than two millimetres long, and 

 are stout, while the spine-like processes have a length of half a 

 millimetre, and are about the same distances apart, being very 

 slender. 



