HERPOIMENIA PLATYPODA. 151 



as all stages of development are represented from a 4-cell condition to advanced 

 larvae where the shell and foot are indicated, the fore and mid gut clearly differ- 

 entiated, the anterior pedal gland developed and to some extent functional, 

 the central nervous system partly mitlined (Plate 22, fig. 7). A fuller account 

 of the embryology is planned for a later paper. 



The brain, of usual size, holds the customary position above the pharynx. 

 The anterior nerves passing to the cirri, etc., and the pedal, lateral, and buccal 

 connectives have the usual relations. Anteriorly the pedal cords enlarge and 

 are united by a more than usually heavy commissure, and each gives rise to a 

 nerve that passes to the wall of the outlet of the anterior pedal gland. Here and 

 there pedal commissures may be detected, as well as connectives with the lateral 

 cords, but these are usually small and often very difficult (o follow. 



The labio-buccal connectives are imbedded in the walls of the pharynx and 

 connect with ganglia, of rather small size, located at the sides of the radula. 

 These ganglia are united by a conmiissure ventral to the pharynx posterior to 

 the radula. The ganglia, and more anteriorly the comiectives, give rise to small 

 fibres that may form commissures, as in other species, Init their lack of sharpness 

 renders it impossible to trace them more than a short distance into the pharyn- 

 geal wall. 



In the posterior end of the body the pedal nerves diminish in calibre and 

 disappear beneath the shell gland. The lateral nerves, upon reaching the 

 forward border of the shell gland, pass diagonally inward toward the mid line 

 until they reach the level of the outlets from the pericardium. Here they en- 

 large (Plate 3, fig. 5) and are united l)y a conmiissure passing dorsal to the rectum. 

 The last two connectives between the jiedal and lateral cords are of about twice 

 the usual diameter and pass to the inner side of the shell gland. From the 

 posterior superior ganglion several nerves arise that course over the cloacal 

 passage to which they give off delicate fibres, then extend into the somatic 

 musculature and probably are distributed in part to the hypodermis. Near 

 the mid dorsal line two other nerves originate and attached to the forward wall 

 of the cloaca j)ass dorsally and are distributed through the somatic musculature 

 in close proximity to the hypodermis. 



Herpomenia platypoda, sp. nov. 



Eleven specimens of this species were taken in the neighborhood of Agattu 

 Island of the Aleutian chain (Sta. 4781) in water 482 fath. in depth. All were 

 attached (Plate 1, fig. 4) to a colony of some unidentified campanularian hydroid 



