No. 1596. DALMANELLAS OF THE CHEMUNG—WILLIA MS. 51 
evidence in hand the radiating lines of )). danbyi appear to be slightly 
angular while in well preserved specimens of LD. leonensis they are 
evenly rounded and the spaces between them are flat. The median 
sulcus on the brachial valve and the median carination on the pedicle 
valve are more sharply differentiated from the general slope of the 
surface in D). danbyt than in PD. leonensis. 
The cardinal process on the inside of the brachial valve of D. dan- 
by? is more elongate, the crura are considerably stronger, and the 
internal muscular and vascular markings ‘are in general stronger for 
shells of corresponding size than in D. leonensis. 
The molds of the interior of brachial valves (the condition in which 
the specimens are generally found) may be quickly distinguished 
from D). Leonensis by their strong curae. The curae are much larger 
than the cardinal process; in specimens 10 mm. in length the crurae 
reach anterior from the point of the beak about 2 mm., or are approx- 
imately one-fifth of the length of the shell. The cardinal process 
forms, in the interior molds, a narrow slit of less than half the length 
of the base of the slits representing the curae. In the ordinary form 
of D. danbyt, as well as in all specimens of /). leonensis at present 
examined, the cardinal process is simple. 
In a specimen of the form beta (Dalmanella danbyi, var. beta, new 
variety), from the Dalmanella danbyi zone at West Danby, a faint 
indication is seen of the trifid shitting of the cardinal process on its 
outer side. (See Plate II, fig. 18.) 
The length of this specimen is only 10 mm., but its breadth is 14 
mm. It occurs in the upper part of the Dalmanella danbyi zone 
In association with specimens of the ordinary form alpha of Dalma- 
nella danbyt. It is only about half the size of specimens of Dal- 
manella tioga of the same form, occurring in the strata of the Cayuta 
member not far above. In this form of /. tioga the trifid character 
of the cardinal process is distinct 1n all specimens examined. I have 
regarded this specimen as possibly a young or undeveloped form 
of PD. tioga, but on account of its size and associations it is listed as 
D. danbyi, var. beta. 
In no specimen of the western form, Dalmanella leonensis, has the 
trifid marking of the end of the cardinal process been seen, though 
it is not impossible that well-developed specimens may exhibit this 
character. 
As the shell thickens (shown by the obliteration of the impressions 
of outer striations upon molds of the interior) the interior molds 
of brachial valves show a gradual increase of distinctness in the 
outline of the muscular impressions and the grooves for vascular 
channels over the surface. There is also, coordinate with this de- 
velopment, a contracting of the lateral and front margins forming 
a more gibbous shell. These facts are well exhibited in a series of 
