LOWER LIELDERBERG ROCKS. 
381 
Fig. 4 a. The right valve. Fig. 4 b. The left valve. Fig. 4 c. Profile view. 
These figures are enlarged to four diameters. 
Geological position and locality. In the slialy limestone of the Lower Helderberg 
group : Herkimer county. 
Beyrichia trisulcata (n. s.). 
Plate LXXIX B. Fig. 5 a, b. 
Carapace minute, semioval; anterior extremity scarcely narrower than 
the posterior; marked by three transverse furrows which are abruptly 
impressed, the central one being essentially central to the entire valve, 
shorter and broader than either of the others, and very slightly bending 
at its base towards the posterior end. Anterior and posterior furrows 
rectangular to the hinge-line, and reaching nearly to the ventral 
margin; the anterior one reaching more nearly to the ventral margin, 
and curving slightly backwards at its base. The posterior median lobe 
narrower than the anterior median one, and a little more elevated; the 
anterior lobe narrower than either of the others, declining towards the 
antero-cardinal margin, which is flattened. 
Surface very finely granulose. 
This species is distinguished from any other in this group, by its minute size, 
and by the three transverse furrows, the central one of which is conspicuously 
shorter. In some of the specimens there appears to be a slight variation from the 
proportions of the parts as described, but I have thus far observed no essential 
differences. 
Fig. 5 a. A specimen : diameter eight times enlarged. 
Fig. 5 b. Profile view of the same. 
Geological position and locality. In the tentaculite limestone of the Lower Hel¬ 
derberg group : Herkimer county. 
