2 MR. C. TATE REGAN ON THE 



for description ; they represent a new genus, Neostethus, related 

 to Phallostethus, and belong to two new species, N. lankesteri 

 and iV. hicornis. 



Of Neostethus lankesteri there are six specimens, all about 

 30 mm. in total length ; five are adult males and the other is an 

 adult female. They come from the Muar River (brackish-water) 

 and from Singapore. Some features in their structure, such as 

 the number of vertebrae and the general I'elations of the viscera, 

 have been elucidated by prolonged clearing with oil of cloves, but 

 the detailed account of the structure of the male fish is based on 

 the study of a series of transverse sections. Of JV. bicornis there 

 are three examples, two males (21 and 25 mm. long) — one imma- 

 ture, the other nearly adult — and a female of 24 mm. ; these are 

 from Kuala Langat (brackish -water), 



Phallostethus is redescribed and is compared with Neostethus. 



2. Structure of Female Neostethus lankesteri *, gen. et sp. n. 

 a. External Characters. 



Form elongate, strongly compressed. Head rather small ; 

 mouth terminal, strongly oblique, protractile, with one or two 

 series of conical teeth in the jaws ; eyes large, lateral. Scales 

 very similar in structure to those of Panchax ; 34 to 36 in a 

 longitudinal series. Dorsal fin of 5 or 6 rays, above the end of 

 the rather long anal, which has 15 or 16 rays; caudal emar- 

 ginate ; pectorals 10 or 11-rayed, placed rather high. Anus 

 {text-fig. 12, B, a.), genital aperture, and urinary opening behind 

 each other in middle line below bases of pectoral fins ; behind 

 -them abdomen compressed to an edge bearing a rayless fringe 

 (text-fig. 12, B, y'.); just behind anus a pair of papillae (text- 

 fig. 12, B, ^j.) (? vestigial pelvic fins t), one much larger than the 

 other, that partly cover a depression into which the oviduct and 

 ureter open. 



h. Skeleton. 



The skeleton is typically Cyprinodont and essentially similar 

 to that of Panchax, except that the haemal arches of the caudal 

 vertebrae are not expanded, as the air-bladder does not extend 

 back into the tail. The vertebrae number 34 or 35 (15-16-f 19). 



c. Viscera. 



The air-bladder occupies the posterior part of the abdominal 

 cavity ; it is large, simple, and thin-walled, except an anterior 



* I have ventured to name this species in honour of Sir Ray Lankester, K.C.B., 

 F.R.S., to whom I am indebted for many acts of kindness and much sound advice. 

 Moreover, it seems to me not inappropriate that this little fish, whose structure 

 presents more than one problem for the consideration of students of animal mor- 

 phology, should bear the name of the most distinguished morphologist of our time. 



t In PJiaUosteMus the postanal papillaj are supported b)" a pair of minute 

 skeletal elements that may be vestigial pelvic bones. 



