No. 11. — On some Young Stages in the Development of Hippa, 

 Porcellana, and Pinnixa. JB)/ Walter Faxon. 



I. Hippa talpoida. 



During the month of August, 1877, I procured large numbers of Hippa 

 talpoida on the bathing-beach near Nobska Point, Wood's Hole, Massachusetts, 

 the locality made known by Professor S. I. Smith. Among them were many 

 ovigerous females, from which I obtained the first stage of the larva. As a 

 supplement to Professor Smith's paper on the early stages of this animal,* I 

 present the following description and figiires of the fii-st zoea-stage, Smith's 

 series beginning with what he presumes to be the second zoea-stage. 



The carapace (Plate I. Figs. 5, 6, 15) is oval, smooth, strongly convex above, 

 curving downward and inward on the sides. It sends a long blunt process 

 forward below the eye-stalks (Plate I. Fig. 6 b). Behind, it presents a deep 

 sinus for the accommodation of the abdomen (Plate I. Fig. 15 6). Anteriorly 

 it is produced between the eye-stalks into a short, broad, rather blunt rostrum. 

 The carapace has no dorsal or lateral spines. At the points where the lateral 

 spines appear after subsequent moults, there is a thickening of the integu- 

 ment, producing a very sUght bulge on the outer surface, a stronger one within 

 (Plate I. Fig. 15 a). 



The abdomen has nearly the same form as in the later stages of the zoea. 

 It consists of but five segments, counting the telson. The first abdominal seg- 

 ment of the adult is fused with the second or with the thorax, the sixth with 

 the telson. The fourth segment in the abdomen of the larva is considerably 

 wider behind than in front. The telson is quite different from the telson as 

 seen in Smith's figures of the later stages. Its breadth now slightly exceeds 

 its length, and the curve of the sides is such that nearly the maximum width 

 is reached but a short distance from the anterior border. From the middle it 

 narrows slightly posteriorly, to be produced at the posterior angles into a stout 

 tooth. As in the later stages, the convex posterior margin of the telson is fur- 

 nished with spines and minute teeth (Plate I. Figs. 13, 14). The number of 

 spines is the same as in the later stages, namely, twenty-six, the eighth, counting 

 from either side, being the longest ; but the number of denticles between the 

 spines is much less than in the later stages. Starting with the single median 

 denticle, the spines are separated by single denticles until the tenth spine is 



■* The Earlv Stages of Hippa talpoida, with a note on the Structure of the Mandi- 

 bles and ]\I;ixilliB in Hippa and liemipcs. By Sidney I. Smith. Trans. Conn. Acad. 

 III. pp. 311 - 342 ; PI. XLV. -XLVIII. 1877. 



