THE NAUTILUS. 9 



in the young of P. compressum Pme. It cannot be mistaken for 

 any other species. 



Pisidium alleni, n. sp. Mussel rather large, well inflated, oval to 

 ovoid in outline, without any projecting angles, beaks slightly behind 

 the middle, large, prominent, rounded ; scutum and scutellum slightly 

 marked, small ; surface shiny, with irregular stria) and several (4-6) 

 strongly- marked lines of growth, color straw to light yellowish, 

 plumbeous around the beaks in old specimens ; shell and hinge me- 

 dium strong, the latter rather long, cardinal teeth placed on the 

 upper part of the hinge plates, the right angular with the posterior 

 part thicker and grooved, left anterior short, pointed, the posterior 

 oblique, rather long, nearly straight, ligament strong. 



Long. 6.2, alt, 5, diam. 3.8 mm. (100 : 81 : 61). Half-grown 

 specimens are rather different in shape, somewhat oblique, moder- 

 ately inflated, posterior margin subtruncate, beaks markedly low and 

 broad, apparently more posterior ; young mussels are very flat. 



Hab. New England, New York ; Hebron and Buckfield, Oxford 

 county, Me., collected by Mr. John A. Allen ; Franklin county, Me., 

 by Mr. N. W. Lermond ; " N. H." in the collection of Dr. James 

 Lewis (B. Walker's), and that of the Cincinnati Soc. N. H.; Clifton, 

 Staten Island, N. Y., Mr. J. B. Henderson, from Sanderson Smith. 

 Types No. 587 la from Hebron, Me. 



The only species to which this has resemblance is roperi St., which 

 is much smaller, with shell and hinge slighter, and half-grown speci- 

 mens not so oblique, and markedly constant over a wide territory. I 

 take pleasure in naming the species in honor of Mr. J. A. Allen, 

 who has done much good collecting in New England and Ohio. 



(To be continued.) 



OBEOHELIX COLONIES IN COLOKADO. 



BY JUNIDS HENDERSON. 



(Concluded from Vol. XXV, p. 139) 

 OREOHELIX COOPERI (W. G. B.) 



Where the formations were badly cut up by igneous intrusions 

 and displaced by folds and faults, in the neighborhood of Rabbit 

 Ears, and elsewhere, attention was sometimes called to the existence 

 of the calcareous formations in unexpected places by the presence of 



