PLATE IV. 



Fig. 1. Head of Ceraunis pleureoeanthemus and two segments of the thorax. En- 

 larged to two diameters, 

 c. Cephalic cavity. 

 i. Intestinal canal. 

 Fig. 2, Transverse section of the thorax of the same specimen. 

 Fig. 5. Under or ventral surface of the dorsal shell of Ccraurus pleurcxanthemus. 

 This figure is restored from several specimens ; many specimens are 

 entire, but some portion may be concealed by the imbedding matrix 

 filling the various depressions in the ventral surface of the shell. 

 Fig. 6. Longitudinal section of the same, with the outline of the intestinal canal 

 and ventral membrane restored. 

 s. Dorsal shell. 

 h. Hj'postoma. 

 c. Cephalic cavity. 

 V. m. Ventral membrane. 

 i. Intestinal canal. 

 Fig. 3. Abranchia from Calymene senaria. 



a. Support of the spii-al attached to a portion of the basal joint 



of the leg. 



b. Spiral branchiae. 



Fig. 4. Same, from Ceraums pleurcxavihemus. 



Fig. 7. Enrolled Calymene senaria, showing a cast of the interior of the ventral side. 

 Fig. 9. Branchiae of Cyamus Scammoni Dall, attached to the thoracic segments. 

 Fig. 10. Branchia; of Cyamits cliff usus Dall, attached to the thoracic segments. 

 Fig. 8. Longitudinal section of the anterior portion of a Ccraurus pleurcxanthemus, 



with ova enclosed within the visceral cavity. 

 Fig. 8 a. Enlargement of the ova. 



