194 BULLETIN OF THE NATURAL HISTORY SOCIETY. 



This tube was very fragile and is found in fragments, of which the 

 largest indicates an aperture of 8 mm. Taper of the tube 1 in 5. 



This species differs from Hyolithes Americanus in the absence of a 

 lip, and in having the lateral angles more acute than the median angle 

 of the ventral side. It differs from all Orthothecfe described by 

 Walcott (under Hyolithes) in its angular form. It differs from all 

 those described by Holm in the acuteness of the lateral angles, and by 

 the concave form of the ventral slopes near those angles. 



This form of Orthotheca seems not to have survived the Etche- 

 minian time, as no similar one is found in the Cambrian. 



Hyolithes excellens, Bill. PI. III., figs. 3, a to i. 

 This is the leading species of the Etcheminian fauna of Smith 

 Sound. It is a true Hyolithes of advanced type, in which a part of 

 the ventral surface has passed over to the dorsal side. It thus belongs 

 to the " Magnidorsati " section of G. Holm, which this author con- 

 siders the higher section of Hyolithes, sens, strict. In H. excellent the 

 proximal part of the tube has a more triangular section than the 

 distal, and this is seen to be due to the two sides of the tube here 

 possessing their original integrity of form, and no portion of the 

 ventral has passed over to the dorsal side. Hence this species at 

 first was among the Equidorsati, but in growing to maturity became 

 a Magnidorsatus. 



Hyolithes rugosus, n. sp. PI. III. figs. 4, a and h. 



A small, slender species, having the dorsal side flatly rounded, and 

 gently curved towards the ventral side longitudinally. 



The ventral side is marked by prominent transverse ribs, which 

 are closely set on the lower part of the tube, but in the upper fifth 

 are more distant. Surface minutely granulated. Length 11 mm.; 

 width about 3| mm. 



Mr. Walcott has described an object similar to this, but smaller, 



as Hyolithellu8 micans, var. rugosa ; it differs in having a longitudinal 



striation between the ridges of growth, where this species has only a 



granular surface. 



CRUSTACEA. 



Ai'tyctiopsis terranovicus. PI. III., fig. 5 



Each valve of this little crustacean has an oval lenticular form 

 with the widest part one-third from the anterior end. The hinge has 



