THE FISHES OF PORTO RICO. 
59 
DESCRIPTIVE USX OF FISHES KNOWN FROM PORTO RICO. 
Family I. BRANCHIOSTOMIDt-E. The Lancelets. 
Body elongate, lanceolate, compressed, naked, colorless; fins represented by a low fold extending 
along back, with usually a rudimentary fold below, which passes by vent to the abdominal pore. 
Mouth inferior, appearing as a longitudinal fissure, surrounded by conspicuous, rather stiff, cirri. Eye 
rudimentary. Liver reduced to a blind sac of the simple intestine. 
Small, translucent creatures found embedded in sand on warm coasts throughout the world. 
Eight species are now recognized, referable to two or three genera, all very similar in appearance and 
habits. The numbers of the muscular impressions furnish the only characters thus far known by 
which the species can be distinguished. 
a. Gonads (reproductive structures) present on both sides of the median line; anal fin present, with traces of fin-rays; 
no caudal process Branchiostoma, 1 
aa. Gonads present on right side only; anal fin without fin-rays or successive fin-ray chambers; a .ong caudal process 
or tail, about as long as head Asymmetron.2 
Genus 1. BRANCHIOSTOMA Costa. Amphioxus. 
Lancelets with the gonads present on both sides of median line. Anal fin present, with traces 
of rays. Vertebral column not produced backward into a caudal process. 
Six or seven species recognized, found in warm seas, usually buried in sand flats at no great depth. 
Very tenacious of life and enduring considerable mutilation. Of the three American species, only one 
is known from Porto Rico. 
a. Myocommata or muscular bands 58 to 64. 
b. Myocommata behind vent 11 to 18, the formula usually 35+14+12=61 lanceolatum 
bb. Myocommata behind vent 7 to 10, the formula usually 35+14+9=58 caribxum , 1 
1 . Branchiostoma caribseum Sundevall. West Indian Lancelet. 
Muscular bands (myocommata) usually 35 -j- 14 -f- 9= 58; gonads 22 to 26 on each side; tail 
short; extremities attenuate. Usual length 1.75 inches. 
In shallow waters, buried in the sand, from Beaufort, N. C., to the mouth of the La Plata; 
abundant off the Carolina coast and in localities in Florida (Port Tampa), Jamaica, Brazil, etc. 
In the white coral sand at the east, end of the island of Porto Rico, at a depth of 10 to 15 fathoms, 
this interesting little species was fairly abundant. About 10 specimens were obtained at stations 6081, 
6086, 6087, 6093, and 6097, mostly at station '6081. The first four of these stations are between Vieques 
and Culebra islands and the last is off Hucares about 5 miles. The bottom at all was of live coral and 
white sand. One specimen (station 6086) was obtained in the dredge, while all the others were caught 
in the tangle. In many cases the lancelets were still alive when picked out from the meshes of the 
tangle, though they had been subjected to considerable rough treatment. The majority do not exceed 
an inch in length, and the largest is but 1.25 inches long. These are considerably smaller than the 
numerous individuals collected by the Fish Hawk off Port Tampa, Fla., in 1898. 
Branchiostoma caribseum Sundevall, Olfers, Vet. Akad. Forhandl., 12,1853, St. Thomas; Jordan & Evermann, Fishes of 
North and Middle America, 3, 1896. 
Genus 2. ASYMMETRON Andrews. 
Gonads, or reproductive structures, developed on the right side only. Anal fia without fin rays 
or successive fin-ray chambers. A long caudal process. Otherwise as in Branchiostoma. One species. 
