166 PALEONTOLOGY OF NEW YORK. 



convergent, so that the approximate surfaces of the cones are flattened. The 

 basal section of these cones is hemicordate, the anterior extremity being much 

 the narrower, but the upper volutions are more nearly elliptical. The ribbon 

 is broad, being conspicuously so on the anterior curves of the first few volu- 

 tions, each one extending considerably beyond the next following. These 

 anterior curves may be more or less distinctly fimbriated. The loop is com- 

 posed of two processes which are continuations of the primary lamellae without 

 angulation. These processes are situated posteriorly, directed toward the center 

 of the shell, and are, in effect, the starting points of the spirals. They have 

 the following structure : the ribbon maintains its usual width for a consider- 

 able distance within the point of attachment to the crura, then narrows rather 

 abrubtly, the processes ascending as they approach each other. Their termina- 

 tions in mature shells are broadened, thickened, erect and recurved at the tips, 

 having a clavate appearance. In immature growth-stages or undeveloped adult 

 conditions this thickening is absent, the extremities of the processes are in 

 close apposition, or may form a continuous lamella. The muscular impressions 

 consist of four large adductor scars divided by a low median ridge. 



Ovarian pittings and vascular sinuses occur over the inner surfaces of both 

 valves. The latter consist of two main trunks, sending two branches poste- 

 riorly, and two longer, converging branches anteriorly. 



External surface covered with radial plications crossed by concentric growth- 

 lines ; at the crossing of the two series of lines the external layers of the shell 

 may be produced into broad lamellar expansions or hollow spines. 



Shell-substance fibrous, impunctate. 



Type, Anomia reticularis, Linn6. From the Clinton to the Waverly groups 

 inclusive. 



Observations. A great number of brachiopods, whose generic relations were 

 of the most uncertain character, have, in the past, been referred to this genus 

 since the date of its establishment. 



Following closely the foregoing diagnosis will result in eliminating from this 

 group the great majority of species passing under the name of Atrtpa, and in 



