GILBERT AND STAKKS — FISHES OF PANAMA BAY 159 



very narrow. The inner surface of the tube is closely covered with large cup-shaped 

 pits, visible to the naked eye. To these pits the olfactory nerve is distributed; they 

 are undoubtedly the end organs of the nerve. 



Similar pits are developed in the genus Tetraodon {erethizoji, setosui^, aerostaticus, 

 perspicillaris, hispidus), where they occupy the inner surface of the nasal flaps; but 

 they are not found in other genera. The nasal organ of Tetraodon could be formed 

 from that of Guentheridia by cutting through the upper edge of the tube, thus leaving 

 two lobes springing from a common base. 



The American species of Sptheroides, nearly all of which we have examined, 

 have the olfactory tubes with small openings, and without cup-shaped pits on 

 their inner surfaces; the latter are smooth, or are sometimes provided with one or two 

 slight folds of skin. 



291. Guentheridia formosa (Giinther). 



Common at Panama, twelve specimens being secured. In addition to these 

 we have examined six specimens collected by the Albatross at Panama in 1888. 

 We found no young of this form, though the young of Tetraodon hispidus and Spher- 

 oides annulatus were common in the tide-i^ools. 



The color pattern is variable. In some examples the spots are almost evenly 

 distributed over the back and upper part of the sides, with no indication of concen- 

 tric arrangement. Other examples have the spots confluent into smooth concentric 

 rings, arranged with the smallest ring in the middle of the back. Between the 

 examples with scattered spots and those with smooth rings are all intermediate stages — • 

 some with the spots arranged concentrically but not united, some with them more or less 

 united, forming rings with uneven contour. The spots vary also in size. Sometimes 

 they are little more than half the size of the eye, and are separated by interspaces 

 of the gray ground color of about their own width, sometimes they are as large as 

 the eye, or larger, and are so closely set that the ground color shows only as narrow 

 lines between them. In one specimen some of the spots have fused into small irreg- 

 ular rings about twice the size of the eye, and enclose small spots of the ground color. 

 The top of head has transverse rows of spots or solid bars. The latter are some- 

 times united in pairs, forming wider and fewer bars. 



Tetraodon formosus was described from a single specimen from South America. 

 The type description is not detailed, so the identification with this Panama form 

 must be considered provisional, until direct comparison can be made with the type. 



292. Tetraodon hispidus Linnoeus. 



Arothron erethizon Jordan & Gilbert, 1882, p. 631. 



This species is not rare about the rocky islands in Panama Bay, where 

 numerous specimens were obtained, ranging from 15 to 330 mm. long. The long 

 quill-like spines protrude only when the fish is inflated. When retracted, the 

 position of the spines is indicated by the pores in the skin. 



