156 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



our specimens it is divided by a transverse joint into two plates. 

 The anterior plate is calcified only at the postero-ventral angles. 

 The anterior gastric muscles (Plate I, Fig. 1), a pair of heavy flattened 

 muscles, arise from the procephalic processes (which are reniform 

 plates attached to the septa between the eyes and the rostrum) and 

 are inserted upon the anterior end of the anterior portion of the 

 dorsal cardiac plate. 



2. The urocardiac ossicle or posterior dorsal cardiac plate. This 

 is narrower than the cardiac ossicle and inclines downward and back- 

 ward so as to form part of the posterior wall of the cardiac sac. 



3. The prepyloric ossicle or median tooth. This forms the 

 antero-dorsal wall of the pyloric sac. 



4. The pyloric ossicle or anterior dorsal pyloric plate. This plate 

 is covered by the insertion of the posterior gastric muscles which 

 arise from the carapace just in front of the cervical groove and from 

 the internal ridge corresponding to the groove. 



On the upper part of the side of the stomach there are: 



5. The pterocardiac ossicle or anterior dorso-lateral plate. 



6. The zygocardiac ossicle or middle dorso-lateral cardiac plate 

 or lateral tooth. This is an irregular parallelogramic vertical plate 

 whose upper anterior angle is bent outward and downward to articu- 

 late with the lower end of the pterocardiac ossicle and whose upper 

 posterior angle is turned inward nearly to the pyloric ossicle. The 

 inner surface of the lower edge of this plate is heavy and irregular and 

 forms the grinding surface of the lateral tooth. 



7. The anterior dorso-lateral pyloric plate. This is a triangular 

 plate interposed between the lateral tooth and the pyloric plate. 

 The postero-lateral gastric muscle arises from an area of the cara- 

 pace bounded behind by the cervical groove, below by the branchio- 

 cardiac groove, and above by the posterior gastric muscle and, pass- 

 ing inward, forward, and downward, is inserted upon the anterior 

 dorso-lateral pyloric plate. The division between the posterior and 

 postero-lateral gastric muscles and between the pyloric and anterior 

 dorso-lateral pyloric plates seems to be lacking in other forms or to 



